Data & Information
These are most probably the most used word when we talk about computers. Computers process data!
I’d like to define data as the raw facts and figures about any particular topic. Different events generate data such as a purchase on store, the salary distribution in an organization, a child is born and so on. These data are gathered and processed (arranged or calculated) for certain purpose. Data alone is meaningless.
2038, Padam, Paknajol, Admin Section, M etc. do not have any meaning unless they are organized and presented in proper manner.
If data collected are stored in organized way so that you can retrieve (get back) any item quickly, store new items and make corrections on existing items efficiently, such organized collection of data is known as database. A telephone directory, the attendance registers, visiting card album etc are all practical examples of databases. Computer databases are much more efficient than real world databases such as phone book because it is very speedy, accurate and diligent device.
As I already told you – data in itself is meaningless but when you arrange them, make some manipulation, or do some calculation it is turned into information. So, information is also called processed data. Byprocessing you should understand as arranging, manipulating and calculating.
In above example if you can derive “Padam works in Admin Section”, it is information obtained by processing above data. Or “Padam worked in our organization for 30 years” because he joined in 2038. We derived 30 years by calculating his date of joining. 2038 is data but “30 years service duration” is information.
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data (plural of “datum”) are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which information and then knowledge are derived. Raw data, i.e. unprocessed data, refers to a collection of numbers, characters, images or other outputs from devices that collect information to convert physical quantities into symbols.
Bits is the plural form of Bit which stands for Binary digit. There are two binary digits 0 & 1. Because computer stores and processes any data in binary digits most of the space measurement is done counting number of binary digits. This way bit is a unit of measurement. For larger spaces we use bytes, kilobytes, megabytes, gigabytes, terrabytes and petabytes. We will be talking about measurement units ………………….. unit. For now it is sufficient if you are aware that bits is abbreviation of binary digits.
Hard & Soft
The terms hard and soft are used very often with many words such as ware, print, output. I found most of the students (I will call you students rather than candidates as long as you are studying here) did not think about the terms properly.
The term Hard is used to mean something permanent and tangible that you can touch, feel, has weight and volume. Hardware are the machinery of computers – all those devices and parts. Hardcopy output is the paper printout that is permanent. You can touch and feel the printed paper.
On the contrary, the term soft is used with a sense of temporary, virtual – that exists and works but you can’t touch, feel. It does not have weight or volume. Software are the programs that run on computer. They exist only till computer is turned on. Softprint is the print preview on screen. It is exactly same as printout but its not permanent and you can’t touch or feel the preview. Soft output or soft copy output is the screen or projector display and even the sound produced on speaker. All these output are temporary in nature which do not have physical existence.
Well, that’s all for now. Before you proceed to next lesson complete the Activities below:
Run to your nearby bookstore and grab a copy of Class IX & Class X Computer Science text books. You are suggested to get a workbook and practice book too if you can find any.
Things to remember
Any facts and figures collected for some purpose is known as data. Data in itself do not have any meaning
Meaningful presentation of data is known as information. Information is achieved after processing data.
We do not use computers to gather data but they are excellent devices to store, process and retrieve.
Arranging (in ascending/descending or any other order), calculating (add, subtract, multiply, divide or any other computations) or any sort of manipulation on data to derive required information is known as processing.
Bits is the abbreviation (short form) of Binary Digits. 8 bits makes one byte.
Hard is used in computer literature to mean permanent and tangible such as hardware, hard-copy output etc
Soft is used in discussions to mean temporary and intangible such as software, soft-print, soft-copy output.
Trying to trace the history of computers, how far should we go? Computer Science is the youngest discipline among human repository of knowledge. We know, the Internet became popular among general public since 1990s; Mark I, the first computer, was built in 1944; computers have never gone earlier than 20th century?
That’s true, but, because computers are elegant devices for calculation, and if we skip the development of calculating devices, we’ll just puzzle how computers came into existence! And to understand how these devices emerged, you should know the need to calculate and count. Oh! ‘the counting devices‘? How did people start to count?
It’s strange at first to see every book on history of computers points to the ancient times – the time when mankind just developed from Stone Age. Uhh? That’s the beginning of mankind! Does the history of computers go that distant? Yes.
The First Problem – Counting
Life in jungle must be enjoying. Though, they did not have luxury of materials, their brain must be free from all the tensions of today’s world. All they cared was food and shelter. I wish Eve had never eaten that apple!
The quest for easy food drove mankind into the agricultural age. People started to possess properties. When there is something you possess, you need to remember the quantity, type and so on. How many sheep do I have? How could a man express a quantity? Numbers were not invented yet!
Knots in vine and ropes, notches in sticks, scratches made on rocks must be the first counting aid for people at that time. Later on, those scratches on rocks and drawings on ground must have given a way to develop numbers.
Guess, what after the numbers came into existence? Obviously, the need to add and subtract them!
Mechanical Devices – Counting and Calculating
In this section we will learn about the counting and calculating devices that contribute a way through for the development of modern day computers.
Abacus – The first known calculating device
Abacus is a simple wooden box with beads strung which are moved towards the mid-bar to perform calculations. You bring the beads near the bar and count to get result. Obtaining result is a manual process. Thus Abacus is essentially a memory aid rather than truly a calculating device. It is generally agreed that Abacus was invented in China around 2500 BC.
An Abacus is divided into two parts – heaven, the upper deck and earth, the lower deck – divided by a mid-bar. On each string there are two beads on heaven and 5 beads on earth. The value of each bead on heaven is 5 and on earth it is 1. So if you pull one heaven bead and 3 earth bead near the mid-bar, it represented the number 8.
Abacus is about ancient past. When we look upon the modern history, it is 1614 when John Napier inventedLogarithm – a branch of mathematics to multiply and divide extremely large or small numbers. This is considered the principal invention of Napier.
In Computer Science what interests us more about Napier’s invention, in addition to the rule of Logarithm, is Napier’s bones. It is a set of rods (10 rods in a set). Numbers are carved on each rod and can be used to perform multiplication, division with the help of logarithm. These rods were made up of bones, and must be the reason for the name.
Calculation is done by aligning the proper rods against each other and by inspection.
Slide Rule was invented by William Oughtred towards 1620. This device consists of logarithmic scales where one can slide upon other. The sliding rule is aligned properly against other scale and a reading is done through the indicator slide.
Slide rule could be used to perform multiplication and divisions efficiently.
Pascal’s Adding Machine – the Pascaline
17 Century was the most fertile for devising different calculating equipment. Blaise Pascal, at an age of 19 years, designed an adding machine to find the sum of numbers. The machine resulted as his effort to help his father. Pascal’s father worked in tax office and in every evening he had to calculate the sum of collection throughout the day.
It was in 1642 Pascal developed Pascaline which could be used to add, subtract, multiply and divide the numbers by dialing wheels.
Leibnitz’s Calculator – The Stepped Reckoner
German philosopher Gottfried Wilhelm von Leibnitz improved Pascal’s adding machine and made Stepped Reckoner that could even find square roots. This is the first digital mechanical calculator that can perform all four basic arithmetic operations – add, subtract, multiply and divide.
Charles Babbage and his engines
Charles Babbage is considered the father of modern computers. It is his ideas – the idea of input, mill (processing), output and storage – the modern computers followed and been successfully miraculous device! Though he could not complete his Analytical Engine (conceived in 1830s) due to insufficient funding and technological advancement of the day, it proved to be a foundation for the birth of computers.
Babbage however completed a working model of his first machine – The Difference Engine and was awarded by Royal Society. Difference engine implemented the mechanical memory to store results. It was based on the difference tables of squares of the number, and thus the name – Difference Engine.
INTERESTING FACT: Babbage conceived of a computer 100 years earlier. Howard Aikin builds the first computer Mark I based on Babbage’s idea in 1944.
Lady Augusta Ada Lovelace – The first programmer
Lady Augusta Ada Lovelace was a great supporter of Charles Babbage and she convinced him to use binary systems in his engines. Because she devised a way to program Babbage’s engines, she is considered the first programmer.
Ada is the daughter of Lord Byron, a famous English poet.
US Defense developed a programming language and named it ADA to honor her contribution
Dr. Herman Hollerith & his Tabulating Machines
Herman Hollerith invented a tabulating machine for the census of 1880s. He used punched cards to code the numbers and feed them into the machine. That’s why he is considered to be the man to use punched cards practically for the first time. Though Charles Babbage used punched cards for his analytical engine, it was never built and Hollerith was successful in designing a machine that could accept input through punched cards.
Hollerith founded Tabulating Machine Company to build and sell his products and later on it was merged with some other companies to form International Business Machine (IBM) Company. IBM is the largest computer manufacturing company even today.
INTERESTING FACT: Punched cards were originally invented by Joseph Jacquard, a textile manufacturer. He used them to automate the weaving loom. These cards were later used by Charles Babbage in his design of Analytical Engine and Herman Hollerith practically used them for the first time in his Tabulating Machine.
EXTRA DOZE: Calculating devices such as Abacus, Slide Rule, and Napier’s bones etc. were very simple machines that could add, subtract and repeated operation to perform multiplication and division. Though they appear trivial today, they were great invention of that time.
By mechanical part, it means it works by moving wheels and bars. Electronic components do not have any moving parts to perform calculation and can work with the flow of electricity in its circuitry. Because it does not have moving parts, these devices are very low at failure rate.
Electro Mechanical Computers
In 1944 the first electro-mechanical computer Mark -I was built by Howard Aiken with the help of IBM. Mark I, Mark II, and Zues Computers (Z2, Z3) are the examples of Electro Mechanical Computers. Let’s look at Mark I and Z3 computer here.
Mark-I, originally known as IBM Automatic Sequence Controlled Calculator (ASCC), is the first computer of the world. Mark-I is described as the beginning of the era of the modern computer. It was built in Harvard University by Howard H. Aiken.
Mark I was a gigantic computer. It was 51 feet long, 8 feet tall and 2 feet wide which weight 4500 Kg. It could do three additions or subtractions in a second. A multiplication took six seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.
|Mark – I||Howard Aiken||1944||First Computer|
Apart from Mark I and Mark II computers, there are other contemporary computers like Z2 and Z3 (designed by Konrad Zuse) on this category.
The contribution of Zuse was ignored for long due to political reasons. He was a German Engineer and Computer Pioneer. Zuse completed his work entirely independently of other leading computer scientists and mathematicians of his day. Between 1936 and 1945, he was in near-total intellectual isolation.
Improving the basic Z2 machine, Konrad built the Z3 in 1941. It was a binary 22-bit floating point calculator featuring programmability with loops but without conditional jumps, with memory and a calculation unit based on telephone relays.
Zuse’s company (with the Z1, Z2 and Z3) was destroyed in 1945 by an Allied air attack.
In 1947 John Mauchly and J. P. Eckert developed the first general purpose electronic computer – ENIAC. This begins a new era in computing history. Apart from ENIAC, ABC, EDVAC and UNIVAC are some early electronic computers. We will be studying these computers in this section.
Calculating devices were fairly simple aid for human head. Electromechanical calculators were moderately complex. There were wheels, drums and bars that rotate and move to produce result. Because they had some mechanical parts, those devices are called electro-mechanical computers.
Electronic computers, on the other hand, work with the flow of electrons in its different components. Because electronic components are more reliable and speedy, electronic computers are very reliable compared to the earlier computers.
ABC, the first electronic digital computer, was invented by John v. Atanasoff and his assistant Clifford Berry and thus the name Atanasoff Berry Computer (ABC).
Earlier, ENIAC was considered to be the first electronic computer until in 1973 a U.S. District Court invalidated the ENIAC patent. Thus, ABC is the first electronic digital computer. However, because ABC is a special purpose computer and not programmable, ENIAC still is the first general purpose electronic computer.
It is the ABC that first implements the three critical features of modern computers:
ü Using binary digits to represent all numbers and data
ü Performing all calculations using electronics rather than wheels, ratchets, or mechanical switches
ü Organizing a system in which computation and memory are separated.
|ABC||John v. Atanasoff & Clifford Berry||1942||First Electronic Digital Computer|
ENIAC stands for Electrical Numerical Integrator And Calculator. It was developed in 1946 by John Mauchly and John Presper Eckert.
ENIAC is the first general-purpose electronic digital computer. It used to be considered the first electronic computer till 1973 when a U.S. District Court invalidated the ENIAC patent and concluded that the ENIAC inventors had derived the subject matter of the electronic digital computer from Atanasoff. Anyway, it is still the first general purpose electronic computer.
ENIAC used decimal numbering system for its operation and contained 17,468 vacuum tubes, along with 70,000 resistors, 10,000 capacitors, 1,500 relays, 6,000 manual switches and 5 million soldered joints. It covered 1800 square feet (167 square meters) of floor space, weighed 30 tons, and consumed 160 kilowatts of electrical power.
Note: In abbreviation the character ‘C’ in these computers stands for ‘Computer’ or ‘Calculator’. Consider both as correct.
|ENIAC||J.P. Eckert & John Mauchly||1946||First General Purpose Electronic Digital Computer|
EDVAC – Electronic Discrete Variable Automatic computer
Well that’s it – the name itself includes the word ‘automatic’ like ENIAC used the word ‘electronic’. ENIAC must be excited as it was not depending upon mechanical components, so, called it ELECTRONIC!
EDVAC was developed by John Mauchly and John Presper Eckert in 1949 with the help of John von Neumann.
|EDVAC||J.P. Eckert & John Mauchly||1949||Stored Program Computer|
EDSAC – Electronic Delay Storage Automatic Computer
EDSAC (Electronic Delay Storage Automatic Calculator) was an early British computer (one of the first computers to be created). The machine, having been inspired by John von Neumann’s seminal EDVAC report, was constructed by Professor Sir Maurice Wilkes and his team at the University of Cambridge Mathematical Laboratory in England.
EDSAC was the world’s first practical stored program electronic computer, although not the first stored program computer (that honor goes to the Small-Scale Experimental Machine).
|EDSAC||Sir Maurice Wilkes||1949||The first Practical Stored Program Computer|
UNIVAC – Universal Automatic Computer
After the successful development of ENIAC and EDVAC, John Mauchly& J.P. Eckert founded their own company in 1946 and began to work on the Universal Automatic computer.
UNIVAC was the first general purpose commercial computer.
|UNIVAC||J.P. Eckert & John Mauchly||1951||The first general purpose commercial computer|
History of Computer in Nepal
We saw the history of computers and some major innovation and pioneers in the world context. Let’s look at the history of Computers in Nepal now.
Nepal was using a calculating device called Facit to prepare census report 2018 BS (1961). Though the total population at that time was only 96 lakhs, Census Bureau could not give the exact figure of population in different districts. Due to the delay, the five year planning had to be stopped. So, for better and quicker data processing, IBM 1401 was brought on rent (Rs. 1 lakh 25 thousand per month) for the census of 2028 B.S (1971). The census processing was completed in 1 year 7 months and 15 days for 1 crore 12.5 lakhs population.
IBM 1401 however was not sent back to the owner after completing census processing but the government purchased it for further data processing in the Bureau of Statistics.
His Majesty’s Government employed IBM 1401 in agricultural data processing, industrial data processing, inventory of Agriculture Bank, Provident fund and SLC result processing.
In 1994, Mercantile Office Systems and Royal Nepal Academy of Science and Technology contracted an Internet feed from a site in India. Since the transmission was over cable, the quality of the line was very poor and the UUCP connection was not reliable. This effort was commercialized although there were significant losses. Mercantile introduced the Internet and email in 1995 for the first time in Nepal.
Government of Nepal introduced the first IT Policy in 2000 with the vision of positioning Nepal on the global IT map within the next five years. The policy has the broad objective of enhancing employment opportunities and creating a knowledge-based society and knowledge-based industries by ensuring that a large section of society has access to information technology. The policy has adopted a 15-point strategic framework that includes human resource development, promotion of foreign and local investments, legal recognition.
Important Points to Remember
People used to count and calculate using knots in ropes, notches in sticks, scratches on rocks and drawing lines on ground when there were no devices to compute.
Abacus is the first known calculating device. It is believed that Chinese invented Abacus around 3000BC. Abacus has two parts separated by mid-bar. The upper deck is called heaven and lower deck is earth. There are 2 beads in each string in heaven and each has value 5. There are 5 beads on earth where each beads has value 1. Calculation is done by shifting beads towards the midbar.
Napier’s bones was invented by a Scottish mathematician John Napier in 1617. There are 11 rods in a set of Napier’s bones and numbers are engraved in each rod. The rods are aligned properly to read the result using Napier’s bones. They could be used to multiply and divide numbers.
John Napier’s principal invention is Logarithm – a branch of mathematics to multiply and divide very large or very small numbers. Napier invented Logarithm in 1614.
Slide Rule was invented in 1620 by English mathematician William Oughtred. Slide Rule contains two or more sliding scales which can be properly aligned and the result is obtained by inspection. It could be used to multiply and divide numbers.
A French mathematician Blaise Pascal invented an Adding Machine called Pascaline in 1642. It can add or subtract numbers by dialing wheels. Blaise Pascal designed this device to help his father who was a tax officer.
Stepped Reckoner was invented in 1671 by a German mathematician Gottfried Wilhelm von Leibnitz. Leibnitz refined Pascal’s Adding Machine and made Stepped Reckoner capable to add, subtracts, multiply, divide and even find square root.
Punched Card was invented by a French textile manufacturer Joseph Jacquard to automate his weaving loom. These cards later used in computers to feed data.
Charles Babbage designed Difference Engine in 1923 and Analytical Engine in 1933.
Babbage could not complete his engines mainly due to the lack of financial support and technology at that time. However, the concepts proposed for Analytical engine (input, mill and output) matches completely with the input, processing, output model of modern computers. That’s why Charles Babbage is known as Father of Computing.
Lady Augusta Ada Lovelace suggested Babbage to use binary numbering system for his Analytical engine and devised a method of using punched cards to calculate which made her The First Programmer. She was known as enchantress of numbers.
An American census statistician Dr. Herman Hollerith developed a mechanicaltabulatingmachinein1887asthe solution of tabulating problem of 1880s census. He established the Tabulating Machine Company in 1896 to manufacture and sell his inventionwhichlateronconvertedintoInternationalBusinessMachine (IBM)Company.
Hollerith founded Tabulating Machine Company which later merges with other three companies – InternationalTime Recording Company, Bundy Manufacturing CompanyandComputingScale Corporation to form a new company namedComputing TabulatingRecording (CTR) Corporation. In 1917 the company changes its name to International Business Machine (IBM) Co. Ltd.
Mark I is the first computer. Howard Aiken and American computer engineer and mathematician Grace Hoper invented it in collaboration with IBM engineers in 1937. It was an electro-mechanical computer with 18000 vacuum tubes. The machine was 51 ft. long, 8 ft. tall and 3 ft. wide.
Mark I is also known as Harvard-IBM Automatic Sequence Controlled Calculator(ASCC).
ABC (Atanasoff Berry Computer) was built in 1939-42 by John Vincent Atanasoff and Clifford Berry. It was the first electronic computer.
ENIAC (Electronic Numerical Integrator And Calculator) is the first general purpose electronic digital computer developed by John William Mauchly and John Presper Eckert in 1946-55. It used decimal numbering system.
Hungarian mathematician John von Neumann proposed Stored Program Concept in 1945. In his paper he suggested that the data as well as instructions to process those data be stored internally in the machine and binary numbering system be used for machine building.
EDVAC (Electronic Discrete Variable Automatic Computer) was invented by John Mauchly and J.P. Eckert in 1946-49. It was the second stored program computer.
Mourice Wilkes and his team in Cambridge University invented EDSAC (Electronic Delay StorageAutomatic Computer) in 1949. It is the first practical Stored Program computer.
UNIVAC is the first commercially available general purpose electronic digital computer. It was invented in 1951 by John Mauchly and J.P. Eckert.
PDP-8 is the first minicomputer introduced by DEC in 1968
Intel 4004 is the first microprocessor developed by Intel Corporation in 1971. This is also the first commercially available microprocessor.
8 inch memory disk (floppy disk) was introduced by IBM in 1971. First sealed hard disk called Winchester was developed in 1972 by IBM.
MITS Altair 8800 is the first successful personal computer.
Microsoft Corporation founded in 1975 by Bill Gates and Paul Allen. In 1976 Job and Woznik developed the Apple personal computer. In 1984 Apple introduced Macintosh computers.
Apple – I personal computer was launched in 1976 by Apple Company and IBM PC was launched in 1981 by IBM Corporation.
In 1981 Microsoft launched “quick and dirty” DOS operating system
Tim Berner Lee developed World Wide Web and CERN released it in 1991.
Intel Corporation produced Pentium II in 1997, Pentium III in 1999 and Pentium IV in 2000.
An international conference in 1962 classified computers into 5 distinct generations – 3 of which are already passed by and we are in fourth generation now. The fifth generation computers are undergoing research and a few computers of this generation are developed that meets some of the expected feature of fifth generation.
Each generation of computers is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful, and more efficient and reliable devices.
In fact, each computer is classified into different generations based on what electronic component it used. It’s not the time period, nor the model.
I’d included this question in sample test for the participants of eCourse and surprisingly found that many students did the very mistake. Vacuum tubes, transistors, ICs, LSI & VLSI chips are used as switching components or memory and processing devices.
First generation computers used vacuum tubes as switching device and magnetic drum for memory. These computers were often huge, occupying an entire hall.
Because first generation computers used vacuum tubes, they consumed a lot of electricity and produced excessive heat. You require cooling facilities to operate computers. This was the major problem of this generation of computers. Moreover, these tubes burned out because of too much heating and need to be replaced more frequently.
The operation cost of these computers was too expensive.
In first generation computers, the operating instructions or programs were specifically built for the task for which computer was manufactured. The Machine language was the only way to tell these machines to perform the operations. There was great difficulty to program these computers and more when there were some malfunctions.
Since when the first generation computers started?
There are two different views regarding from when the first generation began. Some believe that it started from 1946 when the first computer using valve – ENIAC – was developed. Do you remember how many vacuum tubes ENIAC used?
Some othersargue that we should consider EDSAC as the first computer of first generation because it is the first computer to use stored procedure – a true computer in modern sense. ENIAC was just a calculator! If you consider EDSAC is the first computer of first generation, then 1949 should be the starting of first generation.
Note: There is no fixed and generally agreed date for any of the generations. In fact the computers are classified into different generations based on the switching component and technology rather than time slots. Consider the dates as tentative.
More generally the duration of first generation computers is 1946 to 1954.
Features of First Generation Computers
They used vacuum tubes or valves as main electronic component
They were large in size, slow in processing and had small storage capacity
They consumed lots of electricity and produced excessive heat
They were less reliable than later generation computers
They used machine level language for programming
Examples of First Generation Computers
The vacuum tube was an extremely important step in the advancement of computers. Vacuum tubes were invented the same time the light bulb was invented by Thomas Edison and worked very similar to light bulbs. Its purpose was to act like an amplifier and a switch. Without any moving parts, vacuum tubes could take very weak signals and make the signal stronger (amplify it).Vacuum tubes could also stop and start the flow of electricity instantly (switch).These two properties made the ENIAC computer possible.
In 904, John Ambrose Fleming invented the first practical electron tube called the ‘FlemingValve’. Feming invents the vacuum tube diode.
In 1906, Lee de Forest invented the ‘audion’ later called the triode, an improvement on the ‘Fleming Valve’ tube.
In 1906 the American physicist Lee De Forest invented vacuum tube triode. It was the first three terminal device and enabled amplification and switching of electrical signals. Though it helped to push the development of technology a great deal, it had its own problems. The metal that emitted electrons in the vacuum tubes burned out. It occupied lot of space, consumed much power and produced heat.
In 1947 the three Americanphysicists – John Bardeen, William Shockley, and Walter Brattain – at Bell Telephone Laboratories invented transistors. They received the 1956 Nobel Prize jointly for this awesome invention.Transistors proved to be a much better alternative to the vacuum tubes. They were much smaller, produce low heat and were very reliable. This made it possible to develop computers smaller, efficient and more reliable.
Second Generation of Computers (1955 to 1964)
By 1948, the invention of the transistor greatly changed the computer’s development. Coupled with early advances in magnetic-core memory, transistors led to second generation computers that were smaller, faster, more reliable and more energy-efficient than their predecessors.
The first large-scale machines to take advantage of this transistor technology were early supercomputers –Stretch by IBM and LARC by Sperry-Rand. These machines were costly, however, and tended to be too powerful for the business sector’s computing needs, thereby limiting their attractiveness.
A remarkable improvement realized in this generation was the development of assembly language. Assembly language was abbreviated programming codes to replace the machine language – the difficult binary codes.
Towards the early 1960′s, there were a number of commercially successful second generation computers used in businesses, universities, and government. They contained all the components we associate with the modern day computer: printers, tape storage, disk storage, memory, and stored programs.
One important example was the IBM 1401, which was universally accepted throughout industry. This is the first computer to enter into Nepal as well. Nepal brought this computer for the census of 2028 BS.
It was the stored program and programming language that gave computers the flexibility to finally be cost effective and productive for business use.
CLARIFICATION: The stored program concept means the instructions to run a computer for a specific function (known as a program) were held inside the computer’s memory, and could quickly be replaced by a different set of instructions for a different function.
More sophisticated high-level languages such as COBOL (Common Business-Oriented Language) and FORTRAN (Formula Translator) came into common use during this time, and have expanded to the current day.
Features of Second Generation Computers
Second generation computers used transistors as their main electronic component.
These computers were much smaller, reliable and more powerful
Apart from machine language, assembly language were developed and used in this generation
Some high level languages like COBOL & FORTRAN were introduced towards the end of second generation
The computers of second generation used ‘Stored Program Concept’
Printers, tape storage, disk storage, memory were started from second generation of computers
Processing speed improved to microseconds
Examples of Second Generation Computers
|IBM 7030 Stretch||IBM 1401|
Many people enjoy a misconception that all larger computers are from older generations and small computers are the fourth generation computers. Remember, computers are classified into different generations NOT based on their sizes. Though it is true that the old computers were compelled to be of bigger size (larger components and lack of advanced technology).
The vacuum tubes used in first generation were replaced by transistors in second and which in turn were replaced by ICs (Integrated Circuits) in third generation computers. So, first of all, let’s look at those ICs.
Integrated Circuit (IC) is a small electronic device made out of semiconductor material. The first integrated circuit was developed in the 1950s by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor. – WeboPedia
It is amusing to know that two people thought about the same solution but independently. Here is the interesting story about how Robert Noyce got the patent.
Please check R.C. Khanal’s ‘Computer Concept‘ book. He has nicely explained how these IC Chips are manufactured in ‘Computer Generations’ chapter. Notice the terms silicon, wafers, and photolithography.
So, after the invention of IC Chips, it is possible to integrate thousands of registers, diodes, capacitors and many other electronic components and circuitry in a tiny chip.
Integrated circuits are referred with different names like Chips, ICs, Microchips, and so on.
A tiny chip contains the whole electronic network that performs complex tasks.
Types of Integrated Circuits
SSI (small-scale integration):
Up to 100 electronic components per chip
MSI (medium-scale integration):
From 100 to 3,000 electronic components per chip
LSI (large-scale integration):
From 3,000 to 100,000 electronic components per chip
VLSI (very large-scale integration):
From 100,000 to 1,000,000 electronic components per chip
ULSI (ultra large-scale integration):
More than 1 million electronic components per chip
Third Generation Computers (1964-1971)
The computers using small scale integration circuits (SSI)and medium scale integration circuits (MSI) are under this class. The invention of IC Chips made it possible to greatly reduce the size of computers with improvement in operation speed (nanoseconds) and reliability.
The most noticeable achievement of third generation is the development of operatingsystems. The operating systems allowed the machines to run many different applications. These applications were monitored and coordinated by the computer’s memory.
In 1969 AT&T Bell Laboratories programmers Kenneth Thompson and Dennis Ritchie developed theUNIXoperating system on a spare DEC minicomputer. UNIX was the first modern operating system that provided a sound intermediary between software and hardware. UNIX provided the user with the means to allocate resources on the fly, rather than requiring the resources be allocated in the design stages. The UNIX operating system quickly secured a wide following, particularly among engineers and scientists at universities and other computer science organizations.
User interface devices such as Keyboards&Monitors started from this generation. Similarly, GUI also was started from third generation. These are important development of third generation.
Characteristics of Third Generation Computers
Third Generation Computers were based on integrated circuit (IC) technology.
Third Generation Computers were able to reduce computational time from microseconds tonanoseconds
Third Generation Computers utilized operating systems to centrally control and made it possible for multiple programs to run on a computer
Users interacted with computers through keyboards and mouse rather than traditional punched cards and printers.
Third Generation Computers devices consumed less power and generated less heat. In some cases, air conditioning was still required.
The size of Third Generation Computers was smaller as compared to previous computers
Since hardware of the Third Generation Computers rarely failed, the maintenance cost was quite low.
Extensive use of high-level language became possible in Third Generation Computers.
Manual assembling of individual components was not required for Third Generation Computers, so it reduced the large requirement of labor & cost. However, for the manufacture of IC chips, highly sophisticated technologies were required
Commercial production became easier and cheaper.
|IBM 360……………………………… HP2115|
Fourth Generation Computers
Fourth generation for the computers is the era of blooming in multiple dimensions rather than invention of electronic components. Fourth generation computers use ICs as in third generation. But third generation computers used Small Scale and Medium Scale ICs where as in fourth generation Large Scale ICs (LSI), Very Large Scale ICs (VLSI) and the Ultra Large Scale ICs (ULSI) are used.
As millions of electronic components got integrated in a tiny chip, the computers became very small with increased speed, reliability and reduction in cost.
The size of computer reduced to mini computers and microcomputers. Today, we have laptops, palm tops and pocket PCs.
Probably the most important development in this generation is microprocessor. The Intel4004 chip, developed in 1971, took the integrated circuit one step further by locating all the components of a computer (central processing unit, memory, and input and output controls) on a minute chip. Whereas previously the integrated circuit had had to be manufactured to fit a special purpose, now one microprocessor could be manufactured and then programmed to meet any number of demands. Soon everyday household items such as microwave ovens, television sets, and automobiles with electronic fuel injection incorporated microprocessors
In this generation mini computers were built that had more user friendly software packages like word-processor and spreadsheet calculation.
In 1981, IBM introduced its personal computer (PC) for use in the home, office and schools. Other companies made the clones of IBM PCs to make the personal computers more affordable.
In 1984 Apple developed its Macintosh line. Notable for its user-friendly design, the Macintosh offered an operating system that allowed users to move screen icons instead of typing instructions. Users controlled the screen cursor using a mouse.
Fourth generation is the duration when we saw the tremendous improvement in operating systems and high level programming language.
As the small computers become powerful, it was possible to link and work in cooperative environment. This led to the invention of networking. WAN, MAN, LAN and PAN networks came into existence.
Fifth Generation Computers
Up to the fourth generation we saw how computers evolved as the switching devices improved. Fifth generation computers are future computers.
In 1982 Japan started a project named Fifth Generation Computer Systems Project (FGCS) initiated to create a “fifth generation computer” which was supposed to perform much calculation using massive parallel processing. The project was to create the computer over a ten year period, after which it was considered ended and investment in a new, Sixth Generation project, began. Opinions about its outcome are divided: Either it was a failure, or it was ahead of its time. Anyway, it’s out of our context for the moment. I just wished to make you aware you of this fact.
Fifth generation computers are anticipated new type of computer based on emerging microelectronic technologies with high computing speeds and parallel processing. Other major expectations out of this generation are the ability to use natural language and acquire artificial intelligence (AI). Computers will be able to learn by its experience. These computers are being made using ULSI (Ultra Large Scale IC) and Bio-Chips.
We can see some development in achieving these features already. Parallel processing, voice recognition systems and some level of intelligence is been already realized.
CLARIFICATION: Use natural language – computers will be able to understand and use the language that we use in speaking rather than the specially structured commands we are still using in computers.
Examples of Fifth Generation Computers
If y are looking for the examples of fifth generation computers, PIM/m, PIM/p, PIM/i, PIM/k, PIM/c are the computers.
Points to Remember
An international conference in1962 divided the development of computers into five distinct generations based on main electronic component used on them.
The computers that used vacuum tubes are first generation computers and they range the date 1946 to 1958.
Vacuum tube diode was first developed by the English physicist Sir John Ambrose Fleming.
Vacuum tube triode was invented in 1906 by the American engineer Lee De Forest.
First generation computers were very large, consumed a lot of power producing excessive heat. They had low level of accuracy and reliability.
Machine language was used to program first generation computers.
Because thousands of vacuum tubes were used, they produced a lot of heat. Cooling facility was required in any room where computers were installed. Vacuum tubes were burnt out frequently andmaintenance cost was very high. This was the main drawback of first generation of computers.
Second generation computers used transistors as their main electronic component. Transistorwas much smaller, produced almost no heat and thus, they had a tremendousimpact in development of computers and other electronic devices.
Second generation computers were developed in 1959 to 1964
Transistors were invented in 1947 by trio Bell Lab scientists – Walter Brattain, John Bardeen, and William Bradford Shockley.
Assembly language was used to program second generation computers.
Magnetic tapes and disks were used as main secondary storage media.
Third generation computers were developed in 1965 to 1974 that used integrated circuits (ICs) also called microchip as main electronic component.
Transistors were invented by two scientists independently in 1958 – Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor Corporation.
Monitors and Keyboards were introduced in third generation for input and output of data.
High level languages were use to program in third generation.
Fourth generation computers are developed during 1975 to 1990 which used LSI and VLSI microprocessors.
Invention of microprocessors is the most startling development in fourth generation.
Personal Computers (PCs) were introduced and are very popular. GUI was developed in fourth generation.
The first microprocessor called Intel 4004 was developed by American Intel Corporation in 1971.
The fifth generation computer project conducted jointly by several Japanese computer manufacturers under the sponsorship of the Japanese government, emphasized artificial intelligence.
Artificial intelligence is the branch of computer science concerned with designing intelligent computer system that possesses reasoning, learning and thinking capabilities resembling those of a human being.
Fifth generation computers will use super conductor technology – Gallium Arsenide chips or Biochips.
Quantum computation and nanotechnology will radically change the face of computers in years to come.
Classification of Computers
In this chapter, we will look at classification of computers – the different types of computers based on different aspects.
Since the first computer, there are different types of computers. Some are to do specific task and some for general purpose – do everything a program can make it to do. Some computers work with continuous signals of the physical quantities such as pressure, temperature, speed, current etc. and some with discrete data or the digital signals. Some computers are really huge in size while others are as tiny that fit in our pockets and palm. There are computers from different companies that work totally different and some work similar to others. So, in this class we’ll try to identify the classes on which each computer can be grouped into – the classification of computers.
Classification of computers based on application
We can identify three different classes if we look upon how a computer works or what they are applied for – Analog, Digital and Hybrid computers.
An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. These computers are used in Hospitals, Air-crafts and so on.
An analog computer can be mechanical analog computer or electronic analog computer. (There can be a confusion that electronic computers are digital but note that there are electronic analog computers too!)
Mechanical analog computers have existed for thousands of years, with the oldest known example being theAntikythera. This is a Greek machine, thought to have been made around 100 BC, designed for calculating astronomical positions. A more recent and common mechanical analog computer is the slide rule.
The HITACHI 240 Analog Computer
Digital computers are the most common class of computers for us because we are using them every day. Digital Computers can be defined as a computer that performs calculations and logical operations with quantities represented as digits, usually in the binary number system.
In digital computers, mathematical expressions are represented as binary digits (0 and 1) and all operations are done using these digits at a very high rate. It means that the computer operates on electrical inputs that have only two states, ON and OFF. These computers are widely used in commercial and control systems. Nowadays when we use the word computer, we mostly refer to a digital computer.
Analog computers worked purely measuring the physical quantities whereas digital computers counted and manipulated the numbers to produce results. There is another class of computers that can take benefit of features of both these two classes, so, known as hybrid computers.
Hybrid computers are computers with combined features of both digital and analog type. Desirable features of analog and digital machines can be combined to create a Hybrid Computer. This type of computer operates by counting as well as by measuring. In other words, the output can be either in the form of numbers or required units of measurement, e.g., an analog device measures patient’s heart beat (ECG). These measures will be converted into digital form and a digital device checks for any abnormality. Further, we can also input digital data like your marks and get digital results like the result of your class. Another example is a Modem. (which converts the digital signals into analog, carryitalongthelineandatthereceivingendagainchangesitbackintodigitalsignal).
EAI 180 hybrid computer
Classification of computers based on size
We’ve already seen how large the computers were and these days we are using very small computers, some even embedded in wrist watch. So, another interesting aspect to classify computers is based on size. If we look at the computers from this perspective, we can group them into three major classes – Mainframe, Mini and Microcomputers.
These are very huge computers. It is interesting how the word ‘mainframe’ came into use. In fact, because the different units of computer were installed in a frame, it started to be called a computer in main frame and today classes of computers are called Mainframe computers.
Mainframe computers are very powerful computers with large memory and processing capabilities. It can support hundreds of users simultaneously.
Mini computers are medium sized computers – much larger than the personal computers we are using and smaller compared to the mainframe computers. These computers can support multiple users simultaneously and is less powerful than mainframe computers.
A Minicomputer was typically a standalone device that was ideal for use by small and medium sized businesses who needed more power and memory than could be obtained with microcomputers, but did not have a need for the resources provided by mainframes. More recently, a minicomputer is thought of in terms of being a server that is part of a larger network.
Those computers that use microprocessor as their central processing unit and are the smallest of the types are the microcomputers. Microcomputers are often called personal computers (PCs) because they are intended to be used by a single person at a time. While mainframe and mini computers can support multiple users simultaneously, it can support only one user at a time.
Micro computers can further be classified into desktop computers (that can fit within the top of a desk), laptops (portable computers that can be operated on your lap) and palmtops (hand held computers).
There is another class of computers too! But I always feel it uncomfortable to list it as a class based on size. Oh! It does not fit anywhere?But there are a group of powerful computers known as Super Computers.
Super Computers are the fastest type of computer and can be the largest too! Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations. For example, weather forecasting requires a supercomputer. Other uses of supercomputers include animated graphics, fluid dynamic calculations, nuclear energy research, and petroleum exploration.
The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently.
Super Computer – Cray I
Classification of computers based on Brand
Brands are specific names that companies use to identify their product against others in the market. There are many companies involved in computer manufacturing. However there are two classes of computers very different in principle itself – the IBM and the Macintosh. There are many other companies that follow the principle of IBM and are called IBM Compatible computers.
These are the computers developed by IBM Company. After Thomas John Watson became president of Computing Tabulating Recording in 1914, he renamed it in 1924 as International Business Machines Corporation (IBM). In 1975 IBM introduced their first personal computer (PC) which was called the Model 5100. Later on IBM teamed up with Microsoft to create an operating systembecause their software division was not able to meet a deadline. They also teamed up with Intel to supply its chips for the first IBM personal computer. When the personal computer hit the market it was a major hit and IBM gained a strong power in electronic computers.
What identifies IBM computers is because of the UPU design. IBM computers use CISC (Complex Instruction Set Computing) CPUs. It uses the Intel chips for its PCs and relied to Microsoft for operating system.
IBM PC 5150
Apple Macintosh Computers
Apple Company was founded by Steve Jobs and Steve Wozniak in 1976. For about $700 someone could buy a computer that they put together, which was called the Apple I. In 1977 the Apple II was introduced. Apple was trying to appeal more to the business world so they designed the Lisa computer that was a prototype for the Macintosh and it cost around $10,000. It featured a ‘never before seen’ graphical interface and the mouse. In 1984, they launched the Macintosh.
IBM used Motorola chips and created a RISC (Reduced Instruction Set Computing) CPU that could run faster than the CISC model of the same MHz rating, so a RISC chip with a MHz rating of 100 could run just as fast as a CISC chip with MHz rating of 133.
Phoenix Technologies went through published documentation of IBM PC to figure out the internal operating system (BIOS) in the IBM. In turn, they designed a BIOS of their own which could be used with IBM computers. Many manufacturers jumped in and started making their own IBM Compatible computers. So, there is a class of computers that work in the same principle as that IBM PCs but are developed by other companies. These computers are generally known as Compatible Computers.
IBM Compatible PCs
Classification of Computers based on Model
We can still classify computers based on another aspect – model. There are three different models of computers already available – XT computers, AT computers and PS/2 computers.
Extended Technology or XT
The extended technology computers used 8006, 8008, 8086, 8088 processors (These are the names of Microprocessors). The period of these computers was from 1975 to 1982. These processors had 4.77 MHz clock speed (these days there are Gigahertz computers). The processors were all of 8-bit. These computers are outdated now by two reasons: first, they do not support the latest software and the second that they had low processing power as well as low storage capacity.
IBM PC XT (IBM 5160)
Advanced Technology or AT
With the advent of 80286 microprocessors in 1982, Advanced Technology computers were introduced. The processors were of 8-bit and 16-bit. The computers using processors like 80286, 80386, and 80486 are the examples. Advanced Technology computers’ period is from 1982 to 1995. With the features of higher speed and larger memory than the XT computers, they support latest versions of available software.
AT computers may have 80286 SX or 80387 DX, 80486 SX, 80486 DX or even Pentium (80586) processors. The AT computers support Co-processor that enhances the processing speed and capability of the main processor to perform large and computations within a short period.
IBM PC AT
Personal System or PS/2
With the advancement of Processors having high clock speed as well as high storage capacity, IBM developed the second generation of personal computers in early 1990s, which used new refined architecture making the computers faster and more powerful than AT computers. The PS/2 processors used VLSI (Very Large Scale Integration) for chip fabrication and their clock speed range from 85 MHz to 1GHz. Generally, PS/2 Computers use 3.5 inch floppy disks and OS/2 operating System. PS/2 computers are widely used in general purpose computation such as word processing, Database Arrangement, Controlling accounts etc.
Points to Remember
Computers can be classified into different groups according to different categories such as principle or application, size and brand.
Analog, Digital and Hybrid are the three classes of computers based on the principle of work.
Super, Mainframe, Mini and Micro are the different classes of computers based on the size.
Apple/Macintosh, IBM PCs, Compatibles are the classes of computers based on the brand.
Analog computer works by processing the continuous analog signals such as heat, pressure, speed etc.
Digital computer works by processing the discrete data.
Digital computers can be divided into two classes – general purpose and special purpose.
Hybrid computers can accept analog signals or digital data to process and produce results.
Super computer is the largest and the most powerful computer. Its speed is generally measured in FLOPS (Floating Point Operations Per Seconds)
Mainframe computer is often referred as “big iron”. Supercomputer can perform a task in really faster speed but mainframe computer can support largest number of tasks in a time instance.
Minicomputer is medium sized computer and thus suitable for large organizations, universities and research institutes.
Microcomputers are the smallest computers. They range from desktop PCs to laptops, notebooks, palmtops, wearable and pocket computers.
Computers manufactured by IBM Company are known as IBM PCs. Apple Company produced Appleand Macintosh computers. All other manufacturers who produced computers based on IBM PC principle are known as compatibles.
Let’s talk the system in this section – the computer system.
The word ‘system’ is not a new term for anybody, I hope. We are using it in many places. Railway system, respiration system, political systems, document management system, operating systems and so on. Then,what then the ‘System’ means?
When we say system, we understand there are many different distinguishable units that work in its own; there is a link, a relationship or connection among those units; and this link is created for a particular objective. Let’s look at transportation systems. There are vehicles, the authorities that create, issue, and monitors licenses, rules, there are passengers, road, and traffic officers etc as different units. The objective of this system can be to ensure comfortable and safe transportation.
A computer system consists of different units. These units have their own functions. They are connected with each other via cables or other medium. These units are connected with a purpose of smooth operation of computer. Computer system has four major units 1. Input Unit, 2.Processing Unit, 3 Output Unit and 4.Storage Unit.
Input Unit Devices
The task of Input Unit is very simple – to input data into the computer. All the devices that somehow enter data in computer are input devices. We type into keyboard to enter data, click on mouse to issue commands (input commands into computers), scan images, record voice, shoot video and many ways a computer gets data into it. So, keyboard, mouse, light pen, joystick, microphone, web cam, video camera etc. all are input unit device. If we look a bit deeper, it is the input unit that accepts the user data, converts it in suitable form (string of binary digits) –known as encoding – so that it can be used by computer.
Central Processing Unit
The task of processing unit is to process data. It obtains data from input unit, performs necessary calculation, comparisons to produce the result. This unit is often called the central processing unit (CPU) and consists of three sub-units – ALU, CU & MU. Processors, co-processors, Memory cards etc. constitute this unit.
ALU stands for Arithmetic and Logical Unit. This is the calculating unit of a computer system. The actual instructions execute in ALU. It performs mathematical manipulation, logical and comparative analysis. By mathematical manipulation, I mean, it performs the operations such as addition, subtraction and multiplication. Similarly by logical and comparative analysis you should understand that it performs logical operations based on AND, OR and NOT functions. Comparative analysis consists of comparison, for example, whether one is equal or less or greater than another number.
CU stands for Control Unit. It is a sub-unit of CPU that controls and directs the flow of information throughout the computer system. So, it is also known as the nerve center of a computer system. It is the job of CU to fetch instructions, decode them and execute.
Primary Memory RAM Module
This is a part of CPU that handles the storage facilities of data. Primary memory is also known as internal memory. It is called primary memory because this is the only unit through which CPU accesses data directly. The examples of primary memory are RAM and ROM. We’ll read about memory in successive sections.
Output Unit Devices
This unit provides results to the user in suitable form. A computer may output as display on monitor, projector or produce sound in speaker, or printout through printer, plotter etc. These are output devices. This unit receives data from processing unit and converts it in suitable form (decodes – contrast with encoder, the input unit) so that the output is in human readable form.
Storage Unit Hard Disk
Storage unit facilitates the data storage in computer so that it can be kept safe for future use. There are two types of storage – primary or main storage and secondary or auxiliary storage. We generally call memory for primary storage and storage for secondary or auxiliary though memory and storage words are used almost interchangeably.
Paper Tapes, magnetic tapes, floppy disk, hard disk, compact disks, Blu-ray disks etc. are some examples of secondarystorage devices.
Storage Unit Devices
Organization of Computer System
We looked on computer system and its different units briefly in this section. I will further explain the major devices on each of these units in next chapter.
Points to Remember
A computer system comprises of 4 different units – Input Unit, Output Unit, Central Processing Unit and Storage Unit
Input unit accepts user data and sends them to processing unit for further action. Input unit is often considered as encoder as it converts the user data into machine readable form.
Keyboard, mouse, trackball, joystick, touchpad, digitizer, light pen, digital camera, webcam, scanners (bar code reader, optical mark reader, optical character reader, magnetic ink character reader), smart card reader, microphone, are some devices of input unit.
When you press a key on computer keyboard, it release a sequence of 8 bit binary codes which is known as scan code. These scan codes are processed according to the ASCII or EBCDIC to determine which key was pressed.
The task of output unit is to derive the final result as meaningful information for the user. output unit is sometime called the decoder as it converts the machine codes back to the human understandable form.
If the output produced by computer is of temporary nature such as sound or display on screen are known as soft copy output and for a permanent nature output such as printout on paper, we callhard copy output.
Monitor, digital projector, speakers, printers and so on are the devices of output unit.
The task of central processing unit is to process data, control and coordinate with all the devices of computer system. It acts as manager of computer resources.
The job of CPU is to fetch instructions, process them and produce some result or resultant information.
Microprocessor is an example of CPU device. The speed of processor is measured in MegaHertz (MHz)
Arithmetic and Logic Unit (ALU), Control Unit (CU) and Primary Memory (PM) are the different sub-units of Central Processing Unit (CPU).
ALU is the digital circuit that performs all the arithmetic calculations such as addition, multiplication and all comparisons operations.
Control Unit is the nerve center of the computer. It tells teh rest of the computer system how to carry out a program’s instructions.
Control unit directs teh movement of electronic signals between teh memory and ALU. It also directs the control signals between the CPU and I/O devices.
Primary memory is the main memory of a computer system. It is called primary or main because the CPU can access the data in it directly.
It is the primary memory where the data as well as instructions to process those data are stored. After execution the intermediate and final results too are stored in primary memory until it goes to the output devices or secondary storage device.
There are two types of memory chips used for primary memory – RAM and ROM. They are used for different purpose in a computer system. Permanent programs and data such as BIOS, POST, Bootstrap Loader are stored in ROM. Temporary programs and data such as user data, operating systems, applications are stored in RAM.
RAM (Random Access Memory) is volatile memory because the data in it are erased automatically when power supply is cut off. Operating system, application programs and user files are loaded in RAM when they are running.
SRAM (Static Random Access Memory) and DRAM (Dynamic Random Access Memory) are the two types of RAM. SRAM is static in nature and DRAM is dynamic as the name itself suggests. This means, the data stored in SRAM are there as long as power supply is provided. But in DRAM data is erased automatically even when power supply is provided. So DRAM must be refreshed periodically (same data must be written again and again if you still need them).
SRAM chips have access time ranging from 10 to 30 nanoseconds. It is faster than DRAM but is more expensive.
DRAM chips have access time around 60 nanoseconds. So, it is slower than SRAM but is cheaper.
ROM is a permanent memory (non-volatile). The programs stored in ROM are known as firmware.
BIOS (Basic Input Output System) contains special instructions and data that tells the computer how to access hard disk and other devices, find operating system and so on.
The contents of ROM are written when manufacturing these chips.
PROM (Programmable Read Only Memory), EPROM (Erasable Programmable Read Only Memory) and EEPROM (Electrically Erasable Programmable Read Only Memory) are the types of ROM.
PROM chips can’t be erased and reprogrammed. EPROM can be erased by exposing it to high intensity ultraviolet light. EEPROM can be easily erased. You need to remove EPROM chips from computer to erase but for EEPROM you don’t need to take it out.
Cache memory is a high speed temporary memory placed between RAM and processor so that Cache along with RAM can cop up with the speed of Processor.
A cache is useful when RAM accesses are slow compared with the CPU speed because cache memory is always faster than main memory. Cache is much more expensive and consumes more power.
All the mass storage devices or back up storage or auxiliary storage devices are secondary memory. These devices are used to store user’s data for future reference. Disks, tapes, pen drives, CDs, DVDs etc are examples of secondary storage or secondary memory.
Hardware Component of Computer System
Here is some common hardware that you’ll find inside a computer:
Motherboard Central Processing Unit (CPU)
Random Access Memory (RAM) Power Supply
Video Card Hard Drive
Optical Drive (i.e. BD/DVD/CD drive) Sound Card
Network Interface Card (NIC) Analog Modem
FireWire/USB Expansion Card
Here is some common hardware that you might find connected to the outside of a computer:
Keyboard Mouse Printer Scanner
The following hardware is referred to as network hardware and various pieces are often part of a home or business network:
Router Network Switch Access Point
Repeater Bridge Print Server Firewall
Network hardware isn’t as clearly defined as some other types of computer hardware. For example, many home routers will often act as a combination of router, switch, and firewall.
Input Devices – Keyboard, Mouse and Scanner
Input Unit Devices
A unit of computer system that brings data and instruction into the computer is input unit. It accepts data or instruction given by user and converts into machine readable code if required. Keyboard and mouse are the most popular input unit devices. Other devices of this unit are: light pen, joystick, tracker ball, microphone, scanners, sensors, graphic tablet, touch screen etc.
The term input is used to describe the process of capturing or collecting raw data, at the beginning of computer based information system, in to a form that is usable by the computer for processing. Sometimes the data is processed right away(online processing), sometimes hours or days later or even longer (batch processing), as a result the data is often stored in a computer usable form, where it can be quickly retrieved at the time of processing with little or no longer intervention.
Input unit devices can be classified into two groups based on whether the data conversion is involved or not – direct input devices and indirect input devices:
Direct Input Devices
In this input method, data is already in machine readable form and thus, no need to convert it. The data is directly feed into computer to process. Some examples of direct input devices are Point of Sales Terminals (POS), Credit Cards, and Scanners etc. Credit card contains a magnetic strip that contains data in machine readable form and when you insert the card into ATM machine, it can directly feed data for processing.
Indirect Input Devices
If the data is in human readable form, it must be converted into machine readable form so that a computer can process it. This process of data conversion is time consuming and error prone that causes a major bottleneck in data processing. Some examples of indirect input devices are: keyboard, mouse and joystick. When you press any key on keyboard, it converts that character into series of electronic pulses and sends to CPU.
Keyboard is a standard input device. It is a data entry platform of a computer. A computer key board is a sophisticated electromechanical component designed to create specialized electronic codes (scan codes) when a key is pressed. These codes are transmitted along the cables to computer system unit or terminal, where the incoming code is analyzed and converted in to the appropriate computer usable code.
Keyboards have five distinct groups of keys:
Standard type writer keys: resembles a typewriter
Function keys: The top row keys from F1 to F10 or F12
Cursor movement keys: Arrow keys, Home, End, PageUp, PageDown
Numeric keys: a keypad at the right to make it easy to enter numbers
Special purpose keys: Ctrl, Alt, Shift, Del, Insert
Keyboard Layout defines the position of keys in a keyboard. QWERTY is the most popular keyboard layout. Dvorak, Colemak, JCUKEN are other keyboard layouts for Latin scripts. Similarly, we have Traditional, Romanized and Nepali keyboard layout for typing Unicode Nepali script. You can change keyboard layout from Regional and Language Settings in Control Panel.
Why are traditional keyboard layout places keys in the QWERTY order? Why they are not alphabetically ordered like ABCDEF….? You’ll really surprise to know that it was developed to make typing harder and inefficient (do some Googling on this topic). Devorak layout is far better in keys arrangement and improves the speed and accuracy of typing, but the more surprising thing is that it is not much common compared to traditional QWERTY.
Types of Keyboard
By now, I hope, you don’t confused types of keyboards as QWERTY, Devorak and so on. They are not type of keyboards but rather the types of keyboard layout. At the same time, I want to make it clear that the type, as our course defines, is not related to switch technology either. We look on the history of keyboard and classify keyboards into four types based on the technology used.
Types of Keyboards
PC/XT, PC/AT, Enhanced and Windows are the four types of keyboard.
PC/XT (Stands for eXtended Technology) keyboards have 83 keys, function keys (F1 to F10) are arranged on left hand side. These keyboards are not compatible with AT keyboards (that means you can’t use them in AT computers).
PC/AT (Stands for Advanced Technology) contains 84 keys as SysRq (System Request) key was introduced. Moreover indicator LEDs for Caps, Scroll and NUM lock are used in AT keyboards.
Enhanced keyboards have 101 to 106 keys based on different language layout.
Windows Keyboards contained 104 to 109 keys based on different language layouts. Win key and Menu key are the addition on the Windows Keyboards.
Windows Enhanced Keyboard
A mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object you can roll along a hard on flat surface. Its name is derived from its shape, which looks like a mouse, its connecting wire that one can imagine to be the mouse tail; and the fact that one must make it scurry along a surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running. Some newer mice also include a scroll wheel for scrolling through long documents.
Mouse was first invented by Douglas Engelbart in 1963.
There are three types of mouse: Mechanical, Opto-Mechanical and Optical. Mechanical mouse has a ball on its underside and sensors detect the direction of ball movement to move the cursor on the screen.Optomechanical mouse are similar to mechanical mouse but they have optical sensors instead of balls in it.Optical mouse uses laser to detect the mouse movement.
If we look at how a mouse is connected to computer, we can find three types of mouse: Serial Mouse, PS/2 Mouse, USB Mouse. Serial mouse connect through RS-232C serial port and it is the simplest of connection. PS/2 mouse connect through PS/2 port and USB Mouse connect through USB port.
There are some wireless mice in use these days. Cordless mouse (wireless mouse) connects to the computer through infrared or radio wave to communicate with computer. Though cordless mouse are more expensive, they can be greatly useful in some situations.
A scanner is a device that captures images from photographic prints, posters, magazine pages, and similar sources for computer editing and display. Scanners come in hand-held, feed-in, and flatbed types and for scanning black-and-white only, or color. Very high resolution scanners can be used if you need to print scanned image in high-resolution, but lower resolution scanners are adequate for capturing images for computer display. Scanners usually come with software, such as Adobe’s Photoshop product, that lets you resize and otherwise modify a captured image.
Drum Scanner, Flatbed Scanner and Hand Scanner are the three different types of scanners.
When it became possible to scan the images and pre-printed pages, the recognition technology emerged that can recognize the text and marks present on the scanned image and convert them into editable form. As per our syllabus we need to learn about OCR, OMR, BCR and MICR scanners. Following are different technology on the topic:
Different marks OMR can read
The OMR technology allows user to read the check boxes – that is the sign affixed in predefined spaces. This technology can be extremely useful to automate the marking of exam papers of objective exams. Specialized software along with OMR can completely automate the checking, marking and tabulating the exam papers.
Handwritten text that ICR can recognize
With ICR technology it is possible to recognize manuscript data in unconstrained or constrained mode when there is usually space among characters. It can be used to entry the forms directly into the computer.
Bar codes that BCR can read
The BCR technology allows the recognition of bar codes printed on retail products, as well as, decoding their content.
It’s the recognition technology for printed and typed texts. When you have any printed page and require it to edit on computer, this technology can be used to input the document into computer and create editable file.
This technology works on pre-printed OCR-A code lines of postal and banking documents;
This technology works on pre-printed OCR-B code lines of postal and banking documents;
MICR CMC7 – E13B Technology
MICR technology can be used to identify the text written by magnetic ink. Magnetic ink is a special type of ink that contains iron particles dissolved in ink. MICR magnetizes the writing and scan it accurately. It can be used to verify the signatures in bank checks.
MICR CMC7-E13B Technology works on pre-printed CMC7 or E13B check code lines.
It allows user to read manuscript data in cursive written (natural writing not in capital letters): what was only imaginary a few years ago, now it’s real. This feature is essential for reading forms that haven’t been expressly designed for the automatic acquisition and contain unconstrained fields, freely written, without any tie.
Output Devices – Monitor, Printer and Plotters
Output Unit Devices
A unit of computer system that sends information out of the computer or the unit of computer system that provides the result of processing to the users is output unit. This unit receives information from CPU and converts into suitable human readable form. Monitor, Plotter, Printer, Projector, Speaker etc. are the output devices.
An output device is any peripheral device that converts machine-readable information into people-readable form such as a monitor, printer, plotter and voice output device.
A computer monitor is also called display screen or video display terminal (VDT). Text and Images are displayed on monitors by individual dots called pixels. A pixel is the tiny blinking material on computer screen that can be turned on and off or made different shades. A pixel is the smallest unit on the screen. The density of dots determines the clarity of the images – known as resolution. A screen resolution 1024 x 768 means that it has 1024 dots in one line and 768 lines in one screen. Another measure of display resolution is a dot pitch.
Computer display can be interlaced or non-interlaced. In case of interlaced technology, it refreshes all odd lines on screen first then all even lines next. Non-interlaced technology refreshes all the lines on the screen from top to bottom. So, the non-interlaced method gives more stable video display and better for eyes but requires twice as much signal information as interlaced.
There are two types of monitors – cathode-ray tubes (CRT) and flat panel display.
Cathode Ray Tube (CRT) Monitors
A cathode ray tube (CRT) is a specialized vacuumtube in which images are produced when an electron beam strikes aphosphorescent surface. Most desktop computer displays make useof CRTs. The CRT in a computer display is similar to the”picture tube” in a television receiver.
CRT monitors are of two types – monochrome and color.
Monochrome monitors have only two colors – one for background and other for the foreground (text). The colors can be white, amber or green on a dark background. While somewhat plain, the use of a single phosphor to generate the single color in each pixel makes it possible for the monitor to provide a very clear and crisp looking display.
A monochrome monitor was very common in the early days of computing, from the 1960s through the 1980s until color monitors became popular. They are still widely used in applications such as computerized cash register systems.
A color monitor is a display peripheral that displays more than two colors. Color monitors implement the RGB color model by using three different phosphors that appear red, green, and blue when activated. By placing the phosphors directly next to each other, and activating them with different intensities, color monitors can create an unlimited number of colors.Color monitors have been developed through following paths:
CGA stands for Color Graphics Adapter. It is a circuit board introduced by IBM and the first graphics standard for the IBM PC. With a CGA monitor, it is harder to read than with a monochrome monitor because the CGA supports much fewer pixels. It supports 4 colors.
It stands for Enhanced Graphics Adapter. EGA is a video display standard that has a resolution of 640 by 350 pixels and supports 16 colors. EGA supports previous display modes and requires a new monitor.
VGA stands for Video Graphics Array. This is a video display standard that provides medium to high resolution. In a text mode, the resolution of this board is 720 by 400 pixels. It supports 16 colors with a higher resolution of 640 by 480 pixels and 256 colors with 320 x 200 pixels.
This is a very high resolution standard that displays up to 65,536 colors. Super VGA can support a 16.8 million colors at 800 by 600 pixels and 256 colors at 1024 by 768 pixels. A high-priced super VGA allows 1280 by 1024 pixels. Larger monitors (17″ or 21″ and larger) with a high resolution of 1600 by 1280 pixels are available. VESA (Video Electronics Standards Association) has set a standard for super VGA.
Flat Panel Displays
Flat panel display LCD Monitor
Portable computers such as a lap top use flat panel displays, because they are more compact and consume less power than CRTs. Portable computers use several kinds of flat panel screens:
Liquid-Crystal Displays (LCDs)
LCD is a display technology that creates characters by means of reflected light and is commonly used in digital watches and laptop computers. LCDs replaced LEDs(light emitting diodes) because LCDs use less power. LCDs are difficult to read in a strong light, because they do not emit their own light. Portable computers wanted to have brighter and easier to read displays.Backlit LCDs are used for the purpose now.
This is a type of LCD display having its own light source provided from the back of the screen. The backlit makes the background brighter and clear, as a result the texts and images appear sharper. However, this still is much less clear than CRTs. Thus, better technology is needed.
Active Matrix LCDs:
This is an LCD display technique in which every dot on the screen has a transistor to control it more accurately. This uses a transistor for each monochrome or each red, green and blue dot. It provides better contrast, speeds up screen refresh and reduces motion smearing.
Electroluminescent (EL) Displays
A flat panel display technology that actively emits light at each pixel when it is electronic charged. This provides a sharp, clear image and wide viewing angle. The EL display type of flat panel is better than LCD.
Gas Plasma Displays
This is also called a gas panel or a plasma panel and is another flat screen technology. A plasma panel contains a grid of electrodes in a flat, gas filled panel. The image can persist for a long time without refreshing in this panel. The disadvantages of the gas plasma displays are that they must use AC power and cannot show sharp contrast.
Different types of printers
A printer is an output device that produces a hard copy of data on to a paper. The resolution of printer output is expressed as DPI (Dots per inch).
Printers can be classified into different types in several ways. There are three types of printers based on the way they print:
Serial printers are also called a character printer. These printers print a single character at a time. They are usually inexpensive and slow.
Line printers can print one line at a time. They are expensive and very fast. Line printers use a band, a chain, etc.
Page printers can print one whole page at a time. Page printers are also called a laser printer because they usually use a laser to produce page images. The print quality of these printers is the best though it is a little bit expensive. The price of the personal laser printer is decreasing gradually.
Similarly, there are two types of printers based on the use of a hammer.
Impact printers use a hammer or pin to hit the carbon ribbon. This forms characters or dots to print images on the paper. Because these printers hit the paper it produces sound and thus they are noisy. Dot-matrix and daisy-wheel printers are the examples of Impact Printers.
Non-impact printers do not touch paper to produce printout. They do not have the hammer and do not hit. The examples of non-impact printer are ink-jet, laser printer, thermal printers and so on.
There are two types of printers based on how they form characters.
Images are formed from groups of dots and can be placed anywhere on the page. They have many printing options and good printing quality. They use PostScript as a standard language for instructing a microcomputer.
These printers print characters into the lines and columns of a page. These printers use predefined set of characters and are restricted in position of characters.
Microcomputers use five kinds of printers. They are daisy wheel printers, chain printers, dot-matrix printers, ink-jet printers, and laser printers.
Daisy Wheel Printer
Daisy-Wheel is a printer mechanism that uses any kind of hub (wheel) having a set of spokes at the margin of the hub. The end of each spoke is a raised image of a type character. When the wheel is turned and the required character is aligned to the print hammer, the character is then struck into a ribbon and onto a paper with the hammer. The wheel can be removed to use a different character set. Daisy-Wheel Printerprints typewriter-like very high quality characters. However, they are slower and less reliable than dot-matrix printers. Microcomputer users seldom use this printer, because the better dot-matrix printers and inexpensive laser printers are available today.
A chain printer uses a printing mechanism that uses character typefaces linked together in a chain. The chain spins horizontally around a set of hammers aligned with each position. When the required character is in front of the selected print position, hammer in that position hits the paper into the ribbon against the character in the chain. This printer is not commonly found around microcomputers, because it is a very expensive, high-speed machine designed originally for mainframes and minicomputers. Chain printers are very reliable and can speed up to 3000 lines per minute.
Chain Printer Mechanism
Dot-matrix printers are printers that write characters and form graphic images using one or two columns of tiny dots on a print head. The dot hammer moving serially across the paper strikes an inked-ribbon and creates images on paper.Dot matrix printers are popular printers used with microcomputers, because the printers are highly reliable and inexpensive. They are used for tasks where a high-quality image is not essential. Many users, however, move from dot printers to laser printers, because the price of laser printers is falling down. Several kinds of dot matrix printers are available with print heads that have 7, 9, 18, or 24 pins.
Ink-jet is a printer mechanism that sprays one or more color of ink at high speed onto the paper and produces high-quality printing. This printer also produces color printing as well as high-quality image. That is, ink-jet printers can be used for variety of color printing at a relatively low cost. Ink-jet printing has two methods: Continuous stream method and drop-on- demand method.
A laser printer is
a printer that uses the electrophotograpic method used in a copy machine. The
printer uses a laser beam light source to create images on a photographic drum.
Then the images on the drum are treated with a magnetically charged toner and
then are transferred onto a paper. A heat source is usually applied to make the
In 1984, Hewlett-Packard introduced the first desktop laser printer, called the LaserJet. The laser printer revolutionized personal computer printing and has spawned desktop publishing.
The laser printer produces high-resolution letters and graphics quality images, so it is adopted in applications requiring high-quality output. Although a high-priced color laser printer is also available in the market, a less expensive, desktop gray scale laser printer is widely used. Recently, the laser printer is gaining its market share dramatically, mainly because the lowered price and the quality.
A plotter is a special-purpose output device that draws images with ink pens. That is, the plotter is a graphics printer for making sophisticated graphs, charts, maps, and three-dimensional graphics as well as high-quality colored documents. It can also produce larger size of documents.
Plotters require data in a vector graphics format that can produce images with a series of lines. There are two main types of plotters:
This is a plotter that has a drum. A paper wraps the drum that rotates to produce plots. Pens in a drum plotter move across the paper while the drum is turning. A drum plotter is usually used to produce smaller drawings.
This is a plotter that has a bed. This is also called a table plotter. The plotter draws graphics on the paper placed on the bed. There are several size of beds. This plotter is usually used for producing large drawings.
System Unit Devices – Motherboard, Processor and Memory
System Unit is the main part of a microcomputer consisting processing unit and devices. A system unit includes a motherboard that holds a microprocessor chip (which is the CPU), memory chips, and expansion slots. The board contains printed electronic circuitry which connects microprocessor with primary storage and other parts. The system unit is housed within the system cabinet known as chassis.
A system unit includes the parts such as Motherboard, Microprocessor, Memory Chips, System Clock, Buses, Ports, Expansion Slots and Cards
A Motherboard or system board is the main circuit board of a microcomputer. It contains the circuitry printed on a flat board. Motherboard connects microprocessor to all other parts of computer and devices attached. Microprocessors, memory modules, BIOS chip and other ROM chips, system clock, display adapters, build-in VGA and NIC, AGP and PCI expansion slots and so on are housed on motherboard.
The expansion slots or sockets in motherboard accept additional expansion Cards often known as daughterboard. In a microcomputer, the motherboard contains the processor, the primary storage chips (or main memory cards), the buses, and all the chips used for controlling the peripheral devices.
|CPU NO. (Word Size in Bits)||CPU SPEED (MHz)||BUS SIZE (Bits)|
A microprocessor is the main component of a microcomputer. It is a processor whose elements are miniaturized into one or a few integrated circuits contained in a single silicon microchip. Microprocessor executes instructions. In a microcomputer, it is a single microchip to hold the central processing unit (CPU). To function as a processor, it requires a system clock, primary storage, and power supply.
Several important lines of PCs use some families of microprocessor chips. Intel and Motorola are the major companies that produce important microprocessors for IBM compatible and Macintosh computers.
The capacity of a
microprocessor chip is represented in word sizes. A word size is the number of
bits (e.g., 8, 16, or 32 bits) that a computer (CPU) can process at a time.
If word has more bits, the computer (CPU) is more powerful and faster. For example, a 16-bit-word computer can access 2 bytes (1 byte = 8 bits) at a time, while a 32-bit-word computer can access 4 bytes at a time. Therefore, the 32-bit computer is faster than the 16-bit computer.
Based on computer architecture, there are two types of microprocessors – RISC and CISC.
CISC stands for Complex Instruction Set Computer. It is pronounced “sisk.” CISC is a computer architecture that has large sets of instructions (micro-codes). CISC machines have several hundred instructions. Intel’s Pentium-chip uses CISC design.
RISC stands for Reduced Instruction Set Computer. RISC is a microprocessor that executes a few number of instructions (micro-codes). This architecture has a small number of instructions built into the circuits and if those basic instructions are made to execute faster, then RISC computers increase performance. Although RISC machines are only around 30% faster than their CISC machines, RISC chips are less expensive to produce. That is, RISC is less expensive per MIPS.
CONTROVERSY: The proponents of RISC claim that its lower cost and speed are an extreme advantage, while the opponents claim its improvements are not great. The opponents believe that new machine languages and greater performance improvements are going to come. Besides, the reduced instructions make software (e.g., compilers) generate more code to do. Thus, the choice is not obvious.
|IBM and IBM Compatibles|
|Model NO.||Word Size||CPU SPEED (MHz)||BUS SIZE (Bits)|
|Pentium Pro||23 bits||150-231||32-64|
Primary memory is built into chips that can hold programs and data either temporarily or permanently. Based on whether they can store data temporarily or permanently, there are two types of memory chips –RAMs and ROMs.
RAM stands for random-access memory. Random- access memory holds the data or instructions that the CPU is presently processing. It is a volatile memory chip meaning the data stored in RAM are temporary. It is erased automatically after some time or when the power supply is cut off. A collection of RAM chips builds primary storage.
Types of RAM
I’ve presented a complete list of RAMs below. Please pay special attention to SRAM and DRAM.
SRAM: Static random access memory can hold data as long as power supply is provided. It uses multiple transistors, typically four to six, for each memory cell but doesn’t have a capacitor in each cell. It is used primarily for cache.
DRAM: Dynamic random access memory can hold data only for few milliseconds. So it must be refreshed periodically. It has memory cells with a paired transistor and capacitor.
FPM DRAM: Fast page mode dynamic random access memory was the original form of DRAM. It waits through the entire process of locating a bit of data by column and row and then reading the bit before it starts on the next bit. Maximum transfer rate to L2 cache is approximately 176 MBps.
EDO DRAM: Extended data-out dynamic random access memory does not wait for all of the processing of the first bit before continuing to the next one. As soon as the address of the first bit is located, EDO DRAM begins looking for the next bit. It is about five percent faster than FPM. Maximum transfer rate to L2 cache is approximately 264 MBps.
SDRAM: Synchronous dynamic random access memory takes advantage of the burst mode concept to greatly improve performance. It does this by staying on the row containing the requested bit and moving rapidly through the columns, reading each bit as it goes. The idea is that most of the time the data needed by the CPU will be in sequence. SDRAM is about five percent faster than EDO RAM and is the most common form in desktops today. Maximum transfer rate to L2 cache is approximately 528 MBps.
DDR SDRAM: Double data rate synchronous dynamic RAM is just like SDRAM except that is has higher bandwidth, meaning greater speed. Maximum transfer rate to L2 cache is approximately 1,064 MBps (for DDR SDRAM 133 MHZ).
RDRAM: Rambus dynamic random access memory is a radical departure from the previous DRAM architecture. Designed by Rambus, RDRAM uses a Rambus in-line memory module (RIMM), which is similar in size and pin configuration to a standard DIMM. What makes RDRAM so different is its use of a special high-speed data bus called the Rambus channel. RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 MBps. Since they operate at such high speeds, they generate much more heat than other types of chips. To help dissipate the excess heat Rambus chips are fitted with a heat spreader, which looks like a long thin wafer. Just like there are smaller versions of DIMMs, there are also SO-RIMMs, designed for notebook computers.
Credit Card Memory: Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.
PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card’s configuration.
CMOS RAM: CMOS RAM is a term for the small amount of memory used by your computer and some other devices to remember things like hard disk settings. This memory uses a small battery to provide it with the power it needs to maintain the memory contents.
VRAM: VideoRAM, also known as multiport dynamic random access memory(MPDRAM),is a type of RAM used specifically for video adapters or 3-D accelerators. The “multiport” part comes from the fact that VRAM normally has two independent access ports instead of one, allowing the CPU and graphics processor to access the RAM simultaneously. VRAM is located on the graphics card and comes in a variety of formats, many of which are proprietary. The amount of VRAM is a determining factor in theresolution and color depth of the display. VRAM is also used to hold graphics-specific information such as3-D geometry data and texture maps. True multiport VRAM tends to be expensive, so today, many graphics cards use SGRAM(synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.
[source: How Stuff Work – computer.howstuffwork.com]
Memory modules are the circuit board containing memory chips. The type of board and connector used for RAM indesktop computers has evolved over the past few years. The first types of memory modules were proprietary.
SIMM:stands for single in-line memory module. This memory board used a 30-pin connector and was about 3.5 x .75 inches in size (about 9 x 2 cm). Later SIMM boards, slightly larger at 4.25 x 1 inch (about 11 x 2.5 cm), used a 72-pin connector for increased bandwidth and allowed for up to 256 MB of RAM.
DIMM:As processors grew in speed and bandwidth capability, dual in-line memory module (DIMM) evolved. With a whopping 168-pin or 184-pin connector and a size of 5.4 x 1 inch (about 14 x 2.5 cm), DIMMs range in capacity from 8 MB to 1 GB per module and can be installed singly instead of in pairs.
RIMM:Another standard, Rambus in-line memory module(RIMM), is comparable in size and pin configuration to DIMM but uses a special memory bus to greatly increase speed.
SODIMM:Many brands of notebook computers use proprietary memory modules, but several manufacturers use RAM based on the small outline dual in-line memory module (SODIMM) configuration. SODIMM cards are small, about 2 x 1 inch (5 x 2.5 cm), and have 144 or 200 pins. Capacity ranges from 16 MB to 1 GB per module. To conserve space, the Apple iMac desktop computer uses SODIMMs instead of the traditional DIMMs.
Sub-notebook computers use even smaller DIMMs, known as MicroDIMMs, which have either 144 pins or 172 pins.
Most memory available today is highly reliable. Most systems simply have the memory controller check for errors at start-up and rely on that. Memory chips with built-in error-checking typically use a method known as parity to check for errors. Parity chips have an extra bit for every 8 bits of data.
The majority of computers sold today use nonparity memory chips. These chips do not provide any type of built-in error checking, but instead rely on the memory controller for error detection.
[Source: How Stuff Works – computer.howstuffworks.com]
ROM stands for read-only memory. A ROM chip is a memory chip that stores instructions and data permanently. Its contents are placed into the ROM chip at the time of manufacture and cannot be modified by the user. A CPU can read and retrieve the instructions and data from the ROM chip, but it cannot change the contents in ROM.
ROM chips usually contain special instructions for computer operations such as ROM BIOS. The variations on the ROM chip are the following:
PROM (Programmable Read-Only Memory):
A permanent storage device that becomes a read-only memory after it is written once by the customer rather than by the chip manufacturer. For example, a software producer can write instructions onto the PROM using special equipment.
EPROM (Erasable Programmable Read-Only Memory):
EPROM is a reusable PROM-chip that can be erased by a special ultraviolet light. EPROM holds its content until erased and new instructions can be written on it.
EEPROM (Electrically Erasable Programmable Read-Only Memory):
EEPROM-chip can be erased, either within a computer or externally, by electric power. The process usually requires more voltage than the common +5 volts used in logic circuits.
EAPROM (Electrically Alterable Programmable Read-Only Memory)
EAPROM is another type of PROM stands for electrically alterable programmable read-only memory. This type of memory can be changed by the computer using special high-current operations. Programming these devices repeatedly (more than 1,000 times) tends to destroy them, so they are used to hold data that rarely changes.
Primary Storage (Memory)
Primary storage (internal storage, main memory or memory) is the
computer’s working storage space that holds data, instructions for processing,
and processed data (information) waiting to be sent to secondary storage.
Physically, primary storage is a collection of RAM chips.
The contents are held in primary storage only temporarily. Capacity varies with different computers. Data or instructions are stored in primary storage locations called addresses.
Apart from motherboard, processor and memory, there are some other system unit devices worth taking a note. I’ve tried to introduce each of those devices below:
The clock is a device that generates periodic, accurately spaced signals. These signals are used for several purposes such as regulation of the operations of a processor or generation of interrupts. The clock circuit uses the fixed vibrations generated from a quartz crystal to deliver a steady stream of pulses to the processor. The system clock controls the speed of all the operations within a computer.
The clock speed is the internal speed of a computer. The clock speed is expressed in megahertzes (MHz). 33 MHz means 33 million cycles per second. A computer processor’s speed is faster if it has higher clock speed. For example, a 100-Mhz processor is four times as fast internally as the same processor running at 25MHz.
PCI Expansion Slots
Expansion slots are receptacles inside a system unit that printed circuit boards (expansion boards) are plugged into. Computer buyers need to look at the number of expansion slots when they buy a computer, because the number of expansion slots decides future expansion. In microcomputers, the expansion slots are directly connected to the bus.
PCI Expansion Cards
Expansion boards are also called expansion cards, controller cards, plug-in boards,adapter cards, orinterface cards.
Expansion boards are printed circuit boards that have many electronic
components including chips. They are plugged into expansion slots.
Expansion boards are connected to peripherals through ports located on the edge of expansion boards. Expansion boards include memory expansion cards (e.g., SIMM), I/O controller cards (e.g., SCSI Card), video display card, sound cards, communications cards, etc.
Expansion slots and expansion boards can be of two types – open architecture and closed architecture
Open Architecture: This architecture is a system whose specifications are made public to encourage third-party vendors to develop add-on products for it. Most microcomputers adopt open architecture. They allow users to expand their systems using optional expansion boards.
Closed Architecture: This is a system whose technical specifications are not made public. With a machine that has closed architecture, users cannot easily add new peripherals.
A port is an external connecting socket on the outer side of the system unit. This is a pathway into and out of the computer. A port lets users plug in outside peripherals, such as monitors, scanners and printers.
Serial ports are external I/O connectors used to attach modems, scanners or other serial interface devices to the computer. The typical serial ports use a 9-pin DB-9 or a 25-pin DB-25 connector. Serial ports transmit bits one after another on a single communications line. Serial lines frequently are used to link equipment that is not located close by.
Parallel ports are external I/O connectors on a computer used to hook up printers or other parallel interface devices. The parallel port uses a DB-25connector. This port transmits several bits simultaneously. Parallel lines move information faster than serial lines do.
A bus is a data pathway between several hardware components inside or outside a computer. It not only connects the parts of the CPU to each other, but also links the CPU with other important hardware. The other important hardware includes memory, a disk control unit, a terminal control unit, a printer control unit, and a communications control unit. The capacity of a bus is expressed as bits. A larger capacity bus is faster in data transfer. For example, a 32-bit bus is faster than an 8-bit bus.
There are three main architectures of Bus – ISA, MCA and EISA.
ISA (Industry Standard Architecture): ISA is pronounced i- suh. This is the original PC bus architecture. It includes the 8-bit (PC, XT) and 16-bit (AT) buses in IBM personal computer series and compatibles. Now, it refers specially to the 16-bit AT bus.
MCA (Micro Channel Architecture): A 32-bit bus used in IBM P/S 2 series and other IBM models. This architecture allows multiprocessing that allows several processors to work simultaneously. Micro channel architecture is not compatible with PC bus architecture.
EISA (Extended Industry Standard Architecture): EISA is pronounced eesa. This is a bus standard for PCs that extends the AT bus (the ISA bus) architecture to a 32-bit bus. This architecture also allows more than one CPU to share the bus. The purpose of EISA is to extend and amend the old ISA standard, so that all existing AT expansion boards can work with an EISA slot.
The performance of a microcomputer is often restrained by the relatively slow video cards and other peripherals, which cannot keep up with today’s fast CPUs. A local bus reduces the performance gap between the high-speed microprocessors and slower hard disks, video boards and other peripherals.
Storage Devices – Magnetic and Optical Disks
Storage Unit Devices
Computers have two different types of storage – primary (temporary) storage and secondary (permanent) storage. Secondary storage means external storage. There are many different types of secondary storage available on the markets today.This storage device includes a magnetic disk, optical disk, magnetic tape and others.
Data is stored in disk in Tracks and Sectors:
Track: The disk surface is divided into several concentric circles called tracks. The thinner the tracks, the more storage capacity of the disk. Data are recorded as tiny spots on these tracks. These tracks are closed concentric circles, not a single spiral. Each track has the same number of bits although the outer tracks are longer than the inner ones.
Sector: The circular tracks are further divided into wedge-shaped sections known as sectors. The fields of data within a particular record are organized according to tracks and sectors on a disk.
Track and Sector
There are two kinds of sectors for a disk –hard sectored disk & soft sectored. The hard sectored disk identifies sectors with some physical marks on the disk, whereas the soft sectored disk identifies sectors with sector identification contained in the recording tracks.
A format program places the sector identification on the disk. When a user buys a disk manufactured without tracks and sectors in place (this kind of disk does not have “Formatted” label on it), he or she must put the tracks and sectors using a format program.
Floppy disks are removable, direct access storage media. Floppy disks are inserted into floppy disk drive to read and write. Floppy disks are flat, circular pieces of Mylar plastic that rotate within a jacket (protective cover).These are also calledflexibledisks,floppies,Diskettesorsimplydisks.
Data and instructions are stored as forms of bits and bytes using theASCIIorEBCDICdatacoding schemes. They are stored as electromagnetic charges on a disk surface. The first floppies were of 8” in diameter.However, the two most common disks are 5 1/4-inch (5.25″) and 3 1/2-inch (3.5″). More efficient size, high storage capacity and sturdier design of a 3.5″ make it popular storage medium for microcomputers till the CDs and pen drive were available.
DS/DD (2S/2D) Disk: DS/DD means Double Sided Double Density. This is a floppy disk recordedonboth of its sides (DS) and has twice the capacity of the prior format (DD). For the IBM and IBM compatible PCs, DD/DS disk usually has 40 tracks on each side and each side contains 9 sectors of 512 bytes each.
DS/DD5.25” disks: 360KB
DS/DD3.5” disks: 720 KB (PCs), 800 KB for Mac formats.
DS/HD Disk: DS/HD means Double Sided High Density. An HD disk has increased storage capacity usually with more tracks per square inch. For IBM and IBM compatible PCs, an HD disk is usually formatted to have 80 tracks on each side. Each side then contains 18 sectors of 512 bytes each – double capacity of a DD disk.
DS/HD5.25” disks: 1.2MB
DS/HD 3.5” disks: 1.44 MB (PCs), 1.44 MB for Mac formats.
A floppy drive is a device used to read data from floppy disks and store data inside it. Floppy drive grabs a disk at its center and spins it inside its plastic jacket. The drive is made up of a box with a slot into which a user inserts a disk. The slot has a drive gate. This drive rotates the disk with a motor inside the drive. Electronic read/write heads “read” data from the disk and “write” data to it while the disk rotates.
A microcomputer usually has internal floppy drives inside the computer cabinet, but it sometimes has external floppy drive, a separate component outside the cabinet.
Hard Disks (Hard Drives)
A hard disk is a magnetic disk made of metal plates and covered with a magnetic recording surface. Hard disks come in removable and fixed varieties that hold from several hundreds of megabytes to several gigabytes. They are tightly sealed to prevent any foreign matter (dust, moist) from getting inside which causes head crash.
A hard disk can be installed in a computer using IDE or SCSI.
IDE(Integrated Drive Electronics): An IDE interface has a disk drive that contains its own controller electronics. The IDE interface is also called an AT and XT interface. IDE-ready motherboards have a 40-pin socket that connects directly to an IDE drive eliminating the use of an expansion slot.
SCSI (Small Computer System Interface): SCSI is an 8-bit-bus peripheral interface for up to seven peripherals. The SCSI bus allows any two devices to communicate at one time (host to peripheral, peripheral to peripheral). SCSI provides high-speed (4MB/sec.), parallel data transfer and multiple peripheral connections while taking only one expansion slot.
This is an average time taken to complete the transfer of data after the request instruction has been enacted. Today’s fast hard drives have access times under 10 milliseconds (ms). Access time is made up of the following four times.
Seek Time: This is the time taken to move an access arm to a certain track on a disk after the computer requests data. Seek time is one of the slowest action that make up most of the access time.
Head Switching Time: The time taken for changing from one read/write head to another to read from or write on another part on a disk.
Search Time: It is also called rotational delay timeor latency time. This is a time required for the read/write head to locate particular position on a track.
Data Transfer Time: This is the time for data to be transferred from the disk to primary storage or vice versa.
Different Forms of Hard Disks
Internal Hard Disk
Internal hard disk is made up of several metallic platters, a motor, an access arm and read-write heads sealed inside a container.
An internal hard disk is
looked like a part of a system unit inside a computer cabinet. There are two
sizes of drives (5.25″ and 3.5″ in a diameter). 3.5″ hard disks are faster
because the access arm travels shorter distances across the diameter of the
Internal hard disks have advantages over flexible disks. They are high capacity and speed. The disadvantage of internal hard disks orhardcards is that they have only a fixed amount of storage and cannot be easily removed.
External Hard-Disk Drives: This is a drive that is not built into the system cabinet of microcomputers. External hard disk drives are treated as peripherals. Using external hard disk drives, we can expand the hard disk capacity when all available drive bays are occupied.
Hard Disk Cartridges: A cartridge is a removable storage module, so a hard disk cartridge contains disks in the module. They can be removed from a dock easily and can give fast access to large data. An internal or external dock is available.
In internal hard disks and external hard disk drives, the storage capacity is fixed, but in the hard disk cartridge, the capacity limitation of storage does not exist. That is, a user may add more cartridges any time.
Removable Drives with Cartridges: Today’s advanced technology allows a new form of removable storage. The technology combines the function of the hard disk drive and the convenience of the hard disk cartridge. This form consists of a removable drive and several cartridges.
The removable drive looks like an external floppy disk drive. And the cartridge resembles a floppy disk and allows users to add 100 MB or 1 GB at a time. It allows an SCSI connection as well as a parallel port connection. Its low cost is a big advantage.
More advanced technology created a new disk storage forms. Optical disk is a disk written and read by laser beam. This optical disk has a great impact on today’s storage technology. Optical disk does not spin, does not need to move access arms and read/write heads, because a laser beam can be moved electronically. The capacity of the storage is considerably greater than their magnetic disk counterparts, and optical disk storage may eventually replace all magnetic tape and disk storage.
Then how do they work? To write data, a laser beam burns tiny cavities into the surface of a disk to mark bits for data. To read the data, a laser beam scans these areas. There are three forms of optical disks available:
CD-ROM: CD-ROM (compact disk read only memory) is an optical disk storage that contains text, graphics and hi-fi stereo sound. CD-ROM is a 4.75-inch optical disk storage that can store around 650 MB of data. CD-ROM disk is almost the same as the music CD, but uses different forms of track for data. A CD- ROM drive can read music CD, but a CD player cannot read CD-ROM. CD-ROM is a read-only disk that cannot be written on or erased by the user. In CD- ROM standard, data (text or pictures) cannot be viewed with audio play simultaneously. CD-ROM XA standard can do.
WORM: A WORM (write once, read many) disk is an optical disk that written on just once by the user’s environment and then cannot be overwritten. A WORM disk is ideal for use as archive because it can be read many times, but the data cannot be erased. The storage capacity of WORM disk ranges from 400 MB to 6.4 GB.
Erasable Optical Disks: This is an optical disk that can be erased and written on repeatedly. An erasable optical disk has a great deal of data capacity. It can store up to 4.6 GB. An erasable optical disk functions like a magnetic disk and has huge capacity, so it will replace the magnetic disk in the future.
A magnetic tape is a tape coated with a magnetic material on which data can be stored. This is a sequential storage device that is usually used for a backup purpose. A magnetic tape is slower than direct access storage such as disk, because it is sequential access storage. The biggest advantage of magnetic tape is the cost. It is much less expensive than magnetic disk and optical disk. An advanced tape backup technology (DAT) is available these days.
Cache (Cache memory): A cache is a specially designed buffer storage used to improve computer performance by reducing access time. It holds instructions and data that are likely to be needed for next operation by the processor. The cache copies frequently accessed data and instructions from primary storage (main memory) or secondary storage (disks).
Disk Cache: A disk cache is in a reserved segment of primary memory or in an extra memory on the disk controller card. It contains a large block of frequently accessed data copied from a disk. The data in a disk cache can be used to fulfill the following data requests from a processor in a high speed. The disk cache lets the processor avoid a slow disk access.
Memory Cache: A memory cache is high-speed memory storage between memory and the CPU. It is smaller and much faster than main memory (primary storage). The memory cache copies blocks of instructions and data from the main memory so that execution and data updating are performed in the higher-speed memory bank.
Points to Remember
A computer system is an integration of different units which comprises of various hardware components and software, firmware as well as humanware.
The tangible parts or the physical components of a computer are known as computer hardware.
The input output devices that are not built into Chassis (CPU box or Main Machine Box) but installed in the periphery of CPU and connected through wires or wireless technology are known as peripheral devices. Keyboard, Mouse, Printers, Scanners and so on are some examples of peripheral devices.
The storage devices such as floppy disks, hard disks, microfilm or microfiche, CD, DVD and Blu-ray disks are called computer media.
Computer collects the data for processing through various input devices.
Computer keyword is the main input device used to input data and instruction into the computer. Based on how the keys are placed, you can find QWERTY, Dvorak and many other keyboard layouts.
Based on the technology and the number of keys in it, there are XT keyboards (83 keys), AT keyboards(84 keys), Enhanced keyboards (101 or more keys) and Windows keyboards (with Start and popup key).Multimedia keyboard is a term popularly used to mean a keyboard that has Play, Pause, Forward, Backward keys to play music directly from keyboard. Please read
Computer Mouse is a small palm sized pointing device that controls the movement of a cursor on the screen. A mouse can be used to select, move and issue different commands in GUI interface.
A mouse can be with one button, two button and three or more button. The mouse with wheel is convenient for scrolling pages.
Trackball is a stationary pointing device that contains a movable ball rotated with a finger or palm. It looks similar to a mouse but we don’t move trackball like a mouse rather, move the ball in it.
Joystick is a popular input device for playing computer games and it is also used in computer aided designing (CAD). It looks like a car gear leaver and controls the movement in screen.
Touch pad is a device for pointing on a computer display with finger. These are popular alternative to mouse in Laptop and portable computers like personal digital assistants (PDAs).
The first touch pad was invented by George E. Gerpheide in 1988.
Digitizer is a device that can be used to trace or copy a drawing or photograph. A special stylus connected to computer is used to trace the item placed on flat digitizing tablet.
Light pen is a light sensitive penlike device used to point to displayed object and to draw images on the screen.
Digital Camera is an electronic device that can be used to capture and store photographs digitally instead of using photographic film like conventional camera. The images can be read by a computer for further editing and modifications.
Webcam is a digital camera capable of downloading images to a computer for transmission over the internet or other network. Webcams typically capture the images as JPEG or MPEG files.
BCR (Bar Code Reader) is a photoelectric scanner that reads the bar codes, or vertical zebra-striped marks printed on product containers. The data is coded into the lines with different thickness and spaces to form bar codes. Bar codes are extensively used supermarkets for inventory control (stock or store management).
Image Scanner is a light-sensing device that transmit images and other printed information into digital form to the computer so that they can be stored or further processed.
There are 4 types of image scanners – flat-bed scanner, sheet-feed scanner, drum scanner and hand held scanner.
Smart Card Reader is an electronic device that reads smart cards. Smart card is a pocket sized card with an integrated circuit (IC) in it. These cards are used as ID cards, payment cards, public transit card, insurance card, SIM cards etc.
Microphone is an input device that capture the voice and sound and sends to the computer to store or further processing.
Computer generated information is presented to the users through various output devices.
Depending upon the nature of output computer produces, it can be hard copy output or soft copy output. The temporary output such as sound played on speaker or image displayed on monitor are soft-copy output. The printout from printer or plotter are hard copy output.
Monitor is an example of VDU (visual display unit). It is a television like device that displays the information generated by computer.
Three basic types of monitors in use these days are – CRT (cathode ray tube) and LCD (liquid crystal display) and LED (Light Emitting Diode)
In CRT monitor, the images are formed when a beam of electrons hits the screen to light up certain pixels to form the image on the monitor.
In LCD monitor the images are formed when liquid crystal particles rearrange and light up to form an image on the monitor.
In LED monitor A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution.
Digital Projector (digital projection display system) is a specialized computer display that projects an enlarged image on a movie screen.
Speakers and Headphones are the voice output devices. They produce the sound received from computer. A sound card in system unit is used to capture as well as play back the recorded sounds.
A Printer is a hard copy output device that produces output in a permanent readable form. Depending upon how a printer works, it may be impact printer or non-impact printer.
In case of Impact Printers, the printing mechanism touches the paper to produce characters or images such as in daisy wheel printer, dot matrix printer.
In case of non-impact printers, the printing is done without physically touching the paper. These printers uses thermal, chemical, electrostatic, laser or inkjet technology to produce printouts. So non-impact printers are less noisy compared to the impact printer.
Drum printer is an impact printer that consists of a solid cylindrical drum. The surface of drum has raised characters in the form of bands. For each bands there is a hammer which strikes the paper along with the inked ribbon to produce printout.
Dot matrix printers uses a movable print head consisting of pins which hits the inked ribbon against paper to produce a dot on paper. The more pins in printing head the better resolution it can offer. The speed of dot matrix is measured in cps (character per second)
Impact printers are better choice when you need to produce carbon copies of a printout.
Inkjet printer is a high quality non impact printer that forms characters by spraying small drops of ink onto the paper. Inkjets are usually inexpensive, quite in operation ad produce high quality output.
A laser printer uses non impact photocopier technology. When a document is sent to the printer a laser beam draws the document on a selenium coated drum using electrical charges. Then it is rolled in toner (dry ink power). The toner adheres the charged image on the drum which is transferred to the paper and fused with heat and pressure.
A plotter is a specialized output device that produces high quality drawings, maps, charts and other form of graphics. Unlike printers, a plotter can draw continuous point to point lines directly from vector graphics files or commands.
There are different types of plotters available – drum plotter, flat bed plotter, electrostatic plotter. Plotters are used for CAE (computer aided engineering), CAD (computer aided design) and CAM (computer aided manufacturing).
Secondary memory supplements primary memory which is long term, non-volatile and facilitates the storage of large volume of data. This memory is also called backing memory or auxiliary memory or storage. Magnetic tapes, magnetic disks, optical disks, flash memory etc. are some examples of secondary memory.
Magnetic tapes are the cheapest computer media that have slow data access and supports only sequential data storage and retrieval. Magnetic tapes are best suited for sequential data and for large backup purpose.
Magnetic disks are the most popular computer media that stores data in a circular disks. Floppies, hard disks, zip disks, super disks are the examples of magnetic disks. Floppy diskettes contain a plastic disk coated with metal oxide whereas in hard disk drive, there are metal disks. Magnetic disks can support both sequential and direct access. They have relatively faster data access than magnetic tapes.
The storage capacity of floppy disks is measured in megabytes (MB), hard disks in gigabytes (GB).
A typical 3.5″ floppy disk holds 1.44 MB of data.
Floppies can be single sided or double sided. Similarly there are low density floppies or high densityfloppy disks. The disk code DD or 2D is used to mean double sided double density. HD or 2HD is used to mean double sided high density.
IBM introduced the first 8″ floppy disk in 1971 which could store 100KB data. Please visit the following link to see all types of floppy disks and important points to remember
A zip drive is a type of removal disk storage that is capable of storing 100MB to 250 MB data. The first zip drive system was introduced by Lomega.
Super disks is a storage technology developed by Imation corporation which very high-density diskettes.
In magnetic disks the surface is magnetized to store data whereas in optical disks the surface is burned so that it can be read using light reflection.
CDs, DVDs, Blu-Ray are some examples of optical disks.
Optical disks have longer media life than magnetic disks and are free from the corruption due to the magnetic or powerful electric fields.
Compact disk (CD) is a small portable round medium made of molded polymer for electronical recording, storing and playing back audio, video, text and other information in digital form. A CD ROM drive uses a low power laser beam to read digitized data that have been encoded onto an optical disk in the form of tiny pits.
A standard CD ROM can hold 700 MB data.
DVD (Digital Versatile Disk) is a high density optical disk. It was invented by Philips, Sony, Toshiba and Time Warner in 1995.
A DVD ROM supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps.
Pen Drive is a portable USB flash memory device that can be used to quickly transfer audio, video and data files from one computer to another. A pen drive consists of a small printed circuit board encased in a plastic or metal casing. Pen drives are also called flash drive or thumb drive.
Memory stick is an electronic flash memory data storage device used for storing digital information. It was launched by Sony in 1998.
A system unit is also called chasis.
Motherboard is a large flat circuit board covered with sockets and other electronic parts, including a variety of chips. It acts as a data path allowing the various components to communicate with one another. External devices such as keyboard, mouse and monitor cannot communicate with teh system unit without the mother board. Mother board is also called system board.
Microprocessor is the complex integrated circuit, containing millions of miniaturized electronic components. A microprocessor consists of several different sections: ALU performs calculations and makes logical decisions; the registers stores temporary information; control unit directs and co-ordinates the activities of the entire computers; buses carry digital information throughout the chip and the computer; local memory supports on-chip computation.
More complex microprocessors often contain cache memory to speed up access to external data storage device.
An expansion port is any connector that passes data in and out of a computer or peripheral device. They are sometimes called Jacks or Connectors.
Serial port, parallel port, accelerated graphics port (AGP), USB port, FireWire port are some of the popularly used ports in a computer.
Serial ports are used to connect mouse, keyboard, modem and many other devices.
Parallel port are mostly used to connect printers.
AGP ports are used to connect monitors. They are able to support high speed graphics and other video input compared to VGA port.
USB ports can be used to connect up to 127 different devices with a single connector.
FireWire ports are used to connect high speed printers and even video cameras to the system unit.
An expansion slot is a long, narrow socket on the motherboard into which you can plug an expansion card.
An expansion card is a small circuit board that provides a computer with the ability to control a storage device, an I/O device. Expansion cards are also called expansion board, controller cards, adapters or daughter board.
Graphics card is an expansion card to generate output images to display. Monitor is connected with graphics card through VGA port.
MODEM card is an expansion card that lets you connect telephone line with computer.
Sound card is an expansion card that enables a computer to manipulate and output sound
Network card is an expansion card which enables computer to physically connect to a local network.
Power supply box is inside system unit which is designed to convert AC 110 V or 230 V power from main to different low voltage DC power outputs for the internal component of computer.
Exhaust fan is a component of system unit responsible for producing a cooling effect inside the power supply.
System clock is a chip that synchronizes the activities of all the parts of a computer. It uses the quartz crystal. Higher the clock speed, the faster the computer. Clock speeds are expressed in MHz or GHz.
System Bus is a set of wires that facilitate communication between different components of motherboard.
Computer Software Concept
This chapter discusses about following topics:
Types of Computer Software
Operating Systems Language and Language Processors
Low Level language Machine Language Assembly language
Assembler High Level Language Compiler Interpreter
Utilities Application Software
Tailored Software Packaged Software WordProcessing Systems
Spreadsheet Systems Database Management Systems
Presentation Systems Graphic Designing Web Browsers
Email Clients Multimedia and Entertainment
Software is the most important component of computer system. Without software, a computer turns into a dead body – a dead slave!
Software is a generic term for organized collections of computer data and instructions, often broken into two major categories: system software that provides the basic non-task-specific functions of the computer, and application software which is used by users to accomplish specific tasks. –
In other words, software is a set of programs, procedures, algorithms and its documentation concerned with the operation of a data processing system. Thus the software contains the instructions that tell a computer what to do and how to do to solve a specific problem.
In general use, by software we understand a group of programs to make a system run. A program contains instructions or commands to perform a task. The term package or suite is used to describe a group of related software.
Types of Software
Software is generally classified into two groups – system software and application software. Some people prefer three types: system, application and utilities.
System software is responsible for controlling, integrating, and managing the individual hardware components of a computer system so that other software and the users of the system see it as a functional unit without having to be concerned with the low-level details such as transferring data from memory to disk, or rendering text onto a display. Generally, system software consists of an operating system and some fundamental utilities such as disk formatters, file managers, display managers, text editors, user authentication (login) and management tools, and networking and device control software.
There are three type of software under system software: Operating Systems, Language & Language Processors and Utilities
An operating system (OS) is a set of software that manages computer hardware resources and provides common services for computer programs. The operating system is a vital component of the system software in a computer system. Application programs require an operating system to function.
The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop – it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.
Operating systems can be classified as follows:
Multi-user operating system : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
Multiprocessing operating system: Supports running a program on more than one CPU.
Multitasking operating system: Allows more than one program to run concurrently.
Multithreading operating system: Allows different parts of a single program to run concurrently.
Real time operating system: Responds to input instantly. General-purpose operating systems, such as DOS, Windows and UNIX, are not real-time.
Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.
As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.
Language and Language Processors
There are 2 types of computer languages: low level language and High level language.
Low Level Language
Machine language and assembly language are called low level language because they are used to write programs that deal with the low level tasks such as transferring data from memory to disk, or rendering text onto a display. Low level language is machine dependent i.e. a program written for one type of computer does not work on other computers. You need to know the details of a computer rather than problem for which you are writing programs.
The lowest-level programming language. Machine languages are the only languages understood by computers. While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers. It is tiresome and error prone to program in machine language. Programmers, therefore, use either a high-level programming language or an assembly language.
Every CPU has its own unique machine language. Because machine language is directly understood by computer you don’t need to convert it to run.
Assembly languages are between machine languages and high-level languages. Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute names for numbers. Machine languages consist of numbers only.
So, assembly language is a much more readable rendition of machine language. It uses mnemonic codes to refer to machine code instructions, rather than using the instructions’ numeric values directly.
Assembly language is the most basic programming language available for any processor. With assembly language, a programmer works only with operations implemented directly on the physical CPU. Assembly language lacks high-level conveniences such as variables and functions, and it is not portable between various families of processors.
Though assembly language is very close to machine language, computer can’t execute it directly. The language translator that can create machine codes out of assembly language is called Assembler.
High Level Language
High level language is a machine-independent programming language, such as C, C++, Java, Perl and COBOL. It lets the programmer concentrate on the logic of the problem to be solved rather than the intricacies of the machine architecture such as is required with low-level assembly languages.
High level languages uses English like statements and mathematical notations. Because a programmer now does not need to remember the machine architecture and operations implemented directly on the physical CPU, high level languages are machine independent. They are often called problem oriented languages orbusiness oriented language.
High level languages were developed towards the end of second generation of computers (COBOL and FORTRAN) and flourished during third and fourth generations. Pascal, C, C++, C#, LISP, Java, Basic etc. are the examples of high level language.
High level language is completely different than what machines can understand. To run a program written in high level language, you need to convert it into machine code. There are two kinds of language processors to convert high level language into machine language – interpreter and compiler.
A compiler is a language processor that converts the instruction of a high level language into machine language as a whole. Programs written in high level language is called source program and after it is converted into machine language by the compiler, it is called an object program.
Compiler checks each statement in the source program to generate machine instructions. Any syntax errors if existing in source program are discovered while analyzing. A source program containing an error cannot be compiled into an object program.
Each high level language has its own compiler. A compiler can translate the programs of only that language for which it is written. For example C++ compiler can translate only those programs, which are written in C++.
An interpreter is a language processor that converts one statement of high level language program at a time. It executes this statement before translating the next statement of the source program. If there is an error in the statement, the interpreter will stop working and displays an error message.
The advantage of interpreters over compilers is that an error is found immediately. So the programmer can make corrections during program development. Thus, interpreters are often used to debug program while debugging.
The disadvantage of interpreter is that it is not very efficient. The interpreter does not produce an object program. It must convert the program each time it is executed. Visual basic uses interpreter.
Utility software is system software designed to help analyze, configure, optimize or maintain a computer. Utility or a tool is the term used for a single piece of utility software. Utility software are also referred to as service program, tool, service routine, or utility routine.
Utility software usually focuses on how the computer infrastructure (including the computer hardware, operating system, application software, and data storage) operates. Utility software is often targeted at technical people with an advanced level of computer knowledge.
You can find utilities in different categories, such as:
Anti-virus utilities scan for computer viruses. Backup utilities can make a copy of all information stored on a disk, and restore either the entire disk (e.g. in an event of disk failure) or selected files (e.g. in an event of accidental deletion). Data compression utilities output a shorter stream or a smaller file when provided with a stream or file. Disk checkers can scan operating hard drive. Disk cleaners can find files that are unnecessary to computer operation, or take up considerable amounts of space. Disk cleaner helps the user to decide what to delete when their hard disk is full. Disk compression utilities can transparently compress/uncompress the contents of a disk, increasing the capacity of the disk. Disk defragmenters can detect computer files whose contents are broken across several locations on the hard disk, and move the fragments to one location to increase efficiency. Disk partitions can divide an individual drive into multiple logical drives, each with its own file system which can be mounted by the operating system and treated as an individual drive. Archive utilities output a stream or a single file when provided with a directory or a set of files. File managers provide a convenient method of performing routine data management tasks, such as deleting, renaming, cataloging, uncataloging, moving, copying, merging, generating and modifying data sets.Cryptographic utilities encrypt and decrypt streams and files. Hex editors directly modify the text or data of a file. These files could be data or an actual program. Memory testers check for memory failures. Network utilities analyze the computer’s network connectivity, configure network settings, check data transfer or log events. Registry cleaners clean and optimize the Windows registry by removing old registry keys that are no longer in use. Screensavers were desired to prevent phosphor burn-in on CRT and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use. Contemporary screensavers are used primarily for entertainment or security. System monitors for monitoring resources and performance in a computer system. System profilers provide detailed information about the software installed and hardware attached to the computer.
Application software, is used to accomplish specific tasks other than just running the computer system. Application software may consist of a single program, such as an image viewer; a small collection of programs (often called a software package) that work closely together to accomplish a task, such as a spreadsheet or text processing system; a larger collection (often called a software suite) of related but independent programs and packages that have a common user interface or shared data format, such as Microsoft Office, which consists of closely integrated word processor, spreadsheet, database, etc.; or a software system, such as a database management system, which is a collection of fundamental programs that may provide some service to a variety of other independent applications.
Software is created with programming languages and related utilities, which may come in several of the above forms: single programs like script interpreters, packages containing a compiler, linker, and other tools; and large suites (often called Integrated Development Environments) that include editors, debuggers, and other tools for multiple languages.
Types of application software:
You can group application software into two categories – tailored or customized software and packaged software. You can find other categories that lie in between the tailored and packaged.
There are many tasks in an organization or office that can be automated by writing specific software programs. For example SLC board has developed its own software solution for result processing. Provident Fund (Sanchaya Kosh) has developed its own software to record, calculate and perform many other operations. All these software developed are known as tailored software.
Tailored software are the applications developed to solve or automate a particular task of an individual or organization.
Tailored software are developed by employing or hiring a system design and development team who perform system study and find best alternative to solve the problem at hand. They analyze, design new system, develop, testing, debugging and implementation. When the software is ready to do its work, it is handed over to the organization.
Many software houses study the general requirement of computer users and develop software packages. Software packages are aimed at solving some common problem such as word-processing, spreadsheet calculation, database management, presentation systems and so on.
Package software are complex and with less bugs because it is developed often by a large professional team. So they are more reliable compared to tailored software.
Microsoft Office Suite, Lotus Suite, Open Office Suite, Adobe Creative Suite etc. and their individual applications are the examples of packaged software.
Categories of packaged software:
WordProcessing Systems – MS Word, Lotus Write, WordPerfect
Spreadsheet Systems – MS Excel, Lotus 123,
Database Management Systems – MS Access, MySql, Oracle, MS SQL Server
Presentation Systems – MS PowerPoint
Graphic Designing – Adobe PhotoShop, CorelDraw
Web Browsers – Internet Explorer, Firefox, Google Chrome
Email Clients – Microsoft Outlook, Eudora Pro
Multimedia and Entertainment –Windows Media Player, xDiv DVD Player, VLC Player, and computer games
Apart from tailored and packaged software there is another software type called customized software. These are the software applications that are modified or customized to meet your specific need after acquiring some pre-built packaged software. For example you can get MS Excel or Access and use its macro feature or write some other add-ins, or extensions, to solve your particular problem. Any software developed this way is known as customized software.
Liveware is a slang term used to denote people using (attached to) computers, and is based on the need for a human, or liveware, to operate the system using hardware and software. It was used in the computer industry as early as 1966 to refer to computer users, often in humorous contexts by analogy with hardware and software. Other words meaning the same or similar to liveware include wetware, meatware and jellyware.
The term firmware is often used to indicate the control programs stored in ROM chips. Typical examples of devices containing firmware are embedded systems, computers, computer peripherals, mobile phones, and digital cameras. The firmware contained in these devices provides the control program for the device.
Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory. Changing the firmware of a device may rarely or never be done during its economic lifetime; some firmware memory devices are permanently installed and cannot be changed after manufacture.
Common reasons for updating firmware include fixing bugs or adding features to the device. This may require physically changing ROM integrated circuits, or reprogramming flash memory with a special procedure. Firmware such as the ROM BIOS of a personal computer may contain only elementary basic functions of a device and may only provide services to higher-level software. Firmware such as the program of an embedded system may be the only program that will run on the system and provide all of its functions.
Cache (pronounced cash) memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip. It is usually a small amount (normally less than 1MB) of high-speed memory residing on or close to the CPU. Cache memory supplies the processor with the most frequently requested data and instructions. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard’s capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.
As it happens, once most programs are open and running, they use very few resources. When these resources are kept in cache, programs can operate more quickly and efficiently. All else being equal, cache is so effective in system performance that a computer running a fast CPU with little cache can have lower benchmarks than a system running a somewhat slower CPU with more cache. Cache built into the CPU itself is referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.
Points to Remember
Computer in itself is nothing more than a slave in a box. Computer hardware is like a dead body which has all the machinery and mechanism but can’t do anything. A computer requires programs and instructions to do each and every tasks.
A set of self-contained instructions that tells a computer how to solve a problem or carry out a task is called a program. A group of programs that are put into a computer to operate and control its activities is called software.
Software are classified broadly into two types – system software and application software. Loosely, you can understand it as all the software developed to help user to perform his/her required tasks are application software. And similarly, all the software developed to operate computer and help it to be able to run user required applications are system software.
System software is a set of programs that organizes, utilizes and controls the hardware in a computer system. It serves as intermediary between hardware and application software. System software supports – running other software, communicating with peripheral devices, development of other types of software, monitoring the use of hardware resources.
Operating systems, utility programs, device drivers and language processors fall into the class of system software.
Operating system is a type of system software that controls and coordinates the internal working of a computer system. The major function of operating system are – provide user interface to the user; manage disks, devices and other resources; provide platform to run other software; load applications as and when user requests.
Microsoft launched GUI operating environment called Windows in November 20, 1985.
Device drivers are the system software that controls a particular type of device installed in computer. Device drivers has instructions to make operating system able to recognize and operate the device. Device drivers work as intermediary between the hardware device and operating system.
Utility software are system software that are designed to help analyze, configure, optimize and maintain the computer system. It performs the specific task related to the management of computer functions, resources, or files as password protection, memory management, virus protection and file compression.
Many operating systems have some utility programs build directly into the operating system itself. Other utility programs are sold separately as software packages that the user must install.
Disk tool kits, data compression utilities, backup utility programs, virus protectors and screen savers are some utility programs.
Disk defragmenters are utilities that analyse the fragmentation (pieces of a file scattered on different location in disk surface) and move the pieces into one place to improve computer performance.
Disk checkers like chkdsk, scandisk can scan the contents of a disk to find files or disk areas that are corrupted in some way.
Disk cleaners can identify files that are unnecessary to computer operation and can delete them on your permission.
Computers can understand instructions that are in machine language. Any program that is not in machine language must be translated into machine language to execute. A program that translates user’s program into machine language are language translators or language processors.
Assembler, compiler and interpreters are the types of language processors.
Assembler translates a program written in assembly language into machine language. It creates a converted file that is executable in computer. Smalltium, MASM, TASAM are some examples of assembler.
Compiler is a language processor that translates a high level language program into machine code in a single operation. It creates machine language file that can be executed in computer. Programming languages like C, C++, Java, FORTRAN uses compilers.
Interpreter is a language processor that translates each statement of user programs in turn into machine code for the computer to execute. Interpreters do not create machine code file but rather run every instruction after it is converted one after another.
Application Software is a class of computer programs that help users to solve their problems. Application software are also known as applications or apps.
Examples of application software are word processors, database programs, web browsers, development tools, drawing, paint, and image editing programs, communication programs.
API (Application Programming Interface) is a formal request for services and means ofnicating with other programs that a programmer uses in writing an application program.
Application software are further classified into packaged software and tailored or customized software.
Packaged software is a generalized set of programs that allows the computer to perform a specific data processing job for the user. Some of the popular packaged software are Microsoft Word, Microsoft Excel, Microsoft Access and so on.
Tailored software or customized software is the software developed to meet the specific requirement of a particular organization, institution or person. Industrial automation software, business software, payroll software of a company, banking software designed especially for a bank, result processing system for SLC exam etc are examples of some customized software.
WordProcessing software allows users to create, edit and format documents.
Database software allows uses to store and retrieve huge amount of data from database quickly.
Spreadsheet software allows uses to perform complex calculation on a large electronic sheet.
Multimedia software allows uses to create, edit and play audio, video media.
Presentation software allows users to create and present information in the form of display slides.
Image editing software allows uses to create and manipulate images, photographs and other graphics objects.
Computer Networking, Internet & Online Services
Computer Network is a collection of distributed intelligent machines that are connected with each other with transmission media for the purpose of data sharing, communication and sharing of computer resources.
Advantages of Networking
There are considerable advantages of establishing a computer network for any organization. That is the reason of increasing popularity of computer networking.
The following are the distinct notes in favor of computer networking.
The computers, staff and information can be well managed
A network provides the means to exchange data among the computers and to make programs and data available to people
It permits the sharing of the resources of the machine
Networking also provides the function of back-up.
Networking provides a flexible networking environment. Employees can work at home by using office computer through networks.
Network services are the thing that a network can do. There are 5 major network services that a computer network can offer – File Services, Print Services, Message Services, Application Services, and Database Services.
File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving.
Printing Services: This service produces shared access to valuable printing devices.
Message Services: This service facilitates email, voice mails and coordinate object oriented applications.
Application Services: This services allows to centralize high profile applications to increase performance and scalability
Database Services: This involves coordination of distributed data and replication.
There can be one or more computers providing these services for a network called servers. Network Serveris a computer in Network that is designated to provide one or more network service. For example file server, database server etc. There are often a server providing more than one service but if there is a server computer that provides one and only one service, it is known as dedicated server.
A computer in network that connects to the server and uses the network services to perform user’s tasks is a client. If a computer network does not have any server computer (peer-to-peer networking) then each nodes are called workstations. A workstation is a node in network that is more powerful and can handle local information processing or graphics processing. A workstation usually has an inexpensive, small hard disk to carry out local tasks.
Some workstations that have no disk drive of their own is known as diskless-workstation or dumb terminals. They terminals completely rely on LAN for their access. Network operating system lets the node work as if all the resources at the server belong to the node itself.
Each device connected to the network is generally known as a node. Each node is connected with cable or wireless technology known as transmission media. Transmission media is a pathway through which data are transmitted in network. We use different types of cables or waves to transmit data. There are two types of transmission media namely: bound transmission media (guided) and unbound transmission media (unguided).
Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable.
Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. Microwave, Radio wave, Infra red are some of popular unbound transmission media.
Bound Transmission Media
Twisted Pair Cable
Twisted Pair Cable
A pair of wires twisted with each other is known as twisted pair cable. A set of four pairs of twisted wires are bundled to form cable. These are the most common medium for LAN. Wires are twisted with each other so as to reduce the interference.
RJ 45 Jack for Twisted Pair Cable
We can find two types of twisted pair cables, namely: Unshielded Twisted Pair Cable (UTP) andShielded Twisted Pair Cable (STP). The twisted pair cable that is protected against electro-magnetic interference (EMI) is known as STP and the one which is not shielded against EMI is called Unshielded Twisted Pair.
Twisted Pair Cable Structure
|1–Jacket2–Shield-braid3–Shield-foil4–Solid twisted pair5–Drain wire|
A solid central conductor surrounded by insulating material and then by a cylindrical shield woven from fine wires is known as co-axial cable. The shield is usually connected to electrical ground to reduce electrical interference. Co-axial cables have broader bandwidth and thus suitable for audio, video data transmission.
Co-Axial Cable Structure
Co-Axial Cable Connectors
A cable with central glass tube covered with protective shield which transmit data using photons is fiber optics cable. These cables transmit data via concentrated bursts of laser beams which are carried through bundles of hair thin glass fibers. They have advantages over electronic cables in transmission speed and volume. This technology has revolutionized telecommunication applications which used electronic cables. Fiber optic cable is free from electro-magnetic interference as well as wire tapping.
Fiber Optic Cable Structure
Fiber Optics Tubes
Match the following types of connectors with the cables to which they are used.
Cable: (a) Thick Coax (100 Base 5), (b) UTP (10 Base-T), (c) Fiber Optics (10 Base-FL) (d) Thin Coax (100 Base 5)
Connectors: (1) AUI, (2) BNC, (3) RJ45, (4) SC or ST Type
Answer:- a -> 1, b -> 3, c -> 4, d -> 2
AUI (Attachment Unit Interface) Connector
BNC Connectors for Co-Axial Cable
RJ45 Connector for Twisted Pair Cables
SC Connector for Fiber Optics Cable
Comparison between BNC and UTP Cables
Difference between twisted pair and co-axial
Comparison between Twisted Pairs and Co-Axial Cable
Unbound Transmission Media
Unbound transmission media extend beyond the limiting confines of cabling. They provide an excellent communication alternative for WANS. The lack of physical restrictions provides larger bandwidth as well as wide area capabilities. Unbound media typically operate at very high frequencies. The three types of unbound transmission media are: Radio wave, Micro wave, Infrared
Radio Wave Transmission
Although Radio waves are prevalent and well understood, we are just beginning to realize their enormous potential as a networking medium. Radio waves can operate on a single or multiple frequency bands.
Microwaves have been used in data communications for a long time. They have a higher frequency than radio waves and therefore can handle larger amounts of data.
Microwave transmission is line of sight (LOS) transmission. The transmit station must be in visible contact with the receive station. This sets a limit on the distance between stations depending on the local geography. Typically the line of sight, due to the Earth’s curvature, is only 50 km to the horizon! Repeater stations must be placed so the data signal can hop, skip and jump across the country.
Microwaves operate at high operating frequencies of 3 to 10 GHz. This allows them to carry large quantities of data due to their large bandwidth.
Advantages of microwaves
They require no right of way acquisition between towers.
They can carry high quantities of information due to their high operating frequencies.
Low cost land purchase: each tower occupies only a small area.
High frequency/short wavelength signals require small antennae.
Attenuation by solid objects: birds, rain, snow and fog.
Reflected from flat surfaces like water and metal.
Diffracted (split) around solid objects.
Refracted by atmosphere, thus causing beam to be projected away from receiver.
Disadvantages of Microwaves
Infrared offers a great unbound photonic solution. Like fiber-optic cabling, infrared communications use light, so they are not bound by the limitations of electricity.
Types of Computer Network
Computer networks fall into three classes regarding the size, distance and the structure namely: LAN (Local Area Network), MAN (Metropolitan Area Network), and WAN (Wide Area Network). A LAN links a small group of functionally similar workstations within a local geographic area such as a series of adjacent cubicles or offices on the same floor. Once the network expands to include other floors or divers office within a metropolitan area, it becomes a MAN. Finally, a WAN is simply a LAN of LANs. WANs expand the boundaries of networking to a global or even galactic scale.
A LAN is a Local Area Network, within a single building or a specific confined space. LANs typically comprise only one transmission media type such as coaxial cable or twisted pair. LANs are characterized by comparatively high-speed communications. These high speeds are possible because LANs use one kind of cable which generally is limited to 5 km or less.
MAN stands for Metropolitan Area Networks. MAN is larger than a LAN and as its name implies, covers the area of a single city. MANs rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media.
The two most important components of MANs are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication.
A wide area network is simply a LAN of LANs. WANs connect LANs that may be on opposite sides of a building, across the country or around the world. WANS are characterized by the slowest data communication rates and the largest distances. WANs can be of two types: an enterprise WAN and Global WAN.
An enterprise WAN connects an entire organization including all LANs at various sites. This term is used for large, widespread organizations such as corporations, universities and governments.
Global WANs also span the world but they do not have to connect LANs within a single organization. The Internet is an example of a global WAN. It connects diverse locations, organizations and institutions throughout the world. Global WANs can be public or private. Private WANs are called Intranet which belongs to an organization. Public WANs are open to everybody so that anybody can connect and use the resources and services available.
The two types of LAN
There are basically two types of Local Area Networks namely: Arcnet and Ethernet.
The term protocol refers to a set of rules and procedures that govern the transmission of messages over a physical networking medium. The most common network protocols are: (a) TCP/IP, (b) IPX/SPX and (c) NetBEUE
Major Network Protocols
The three major network protocols are:
IPX/SPX (Used in Novell Netware)
NetBEUE (Product of Microsoft Co.)
IPX SPX Protocol Structure
Match the following protocols and their functions
(a) http, (b) pop, (c) ftp, (d) smtp, (e) MIME,
1. Send email messages
2. Transfer multimedia information
3. Send email attachment
4. Transfer files in servers and clients computers
5. Receive email messages
Answer: (a) -> 2, (b) -> 5, (c) -> 4, (d) -> 1, (e) -> 3
The term topology defines the geographic arrangement of networking devices. It describes the actual layout of the network hardware. Given the location of workstations and peripherals, the goal of topology is to find the most economical and efficient way to connect all the users to the network resources while providing adequate capacity to handle user demands, maintain system reliability and minimize delay.
Different LAN Typologies
The selection of a topology for a network cannot be done in isolation as it affects the choice of media and the access method used. Because it determines the strategy used in wiring a building for a network and deserves some careful study.
The two network connection types
The two different network connection types are (a) point-to-point connection and (b) multipoint connection.
Point-to-Point connection type
A point-to-point connection is a direct link between two devices such as a computer and a printer. Most of today’s point-to-point connections are associated with modems and PSTN (Public Switched Telephone Network) communications.
A multipoint connection is a link between three or more devices. Historically, multipoint connections were used to attach central CPs to distributed dumb terminals. In today’s LAN environments, multipoint connections link many network devices in various configurations.
Basic LAN Topologies
The three simple LAN topologies that are combined to form any practical topology are known as basic LAN topologies. They are, Bus Topology, Ring Topology and Star Topology.
Explain Bus Topology.
The physical Bus topology is the simplest and most widely used of the network designs. It consists of one continuous length of cable (trunk) and a terminating resistor (terminator) at each end. Data communication message travels along the bus in both directions until it is picked up by a workstation or server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at the terminator.
All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop cables or direct T-connectors. The number of devices and the length of the trunk can be easily expanded.
BUS Topology connected with other network
The Advantages of Bus Topology
The advantages of physical bus topology are:
It uses established standards and it is relatively easy to install.
It requires less media than other topologies.
The Disadvantages of Bus Topology
The disadvantages of bus topology are:
The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached.
They are also difficult to troubleshoot because everything happens on a single media segment. This can have dangerous consequences because any break in the cabling brings the network to its knee.
The physical ring topology is a circular loop of point-to-point links. Each device connects directly to the ring or indirectly through and interface device or drop cable. Message travel around the ring from node to node in a very organized manner. Each workstation checks the message for a matching destination address. If the address doesn’t match the node simply regenerates the message and sends it on its way. If the address matches, the node accepts the message and sends a reply to the originating sender.
Advantages of Ring Topology
The advantages of ring topologies are:
They are very easy to troubleshoot because each device incorporates a repeater.
A special internal feature called beaconing allows troubled workstations to identify themselves quickly.
Disadvantages of Ring Topology
The disadvantages of ring topologies are:
It is considerably difficult to install and reconfigure ring topology
Media failure on unidirectional or single loop causes complete network failure.
The physical star topology uses a central controlling hub with dedicated legs pointing in all directions – like points of a star. Each network device has a dedicated point-to-point link to the central hub. This strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic.
This topology, obviously, require a great deal of cabling. This design provides an excellent platform for reconfiguration and trouble-shooting. Changes to the network are as simple as plugging another segment into the hub and a break in the LAN is easy to isolate and doesn’t affect the rest of the network.
Benefits of Star Topology
The benefits of star topology are:
Relatively easy to configure.
Easy to troubleshoot
Media faults are automatically isolated to the failed segment.
Disadvantages of Star Topology
The disadvantages are considered as follows:
Requires more cable than most topologies.
Moderately difficult to install.
Popular topologies other than basic Topologies
Apart from basic topologies some other topologies worth considering are: mesh topology (every device connected to all other devices), Cellular Topology (wireless point to pint and multipoint design), Tree Topology (Hierarchical connections of devices), Hybrid topology (combination of two or more basic topologies).
Protocol (the logical component) and Topology (the physical component) is combined together to create a networking standard. These standards are developed and controlled by the Institute of Electrical and Electronics Engineers (IEEE).
Major industry standards
The four major industry standards are (a) Ethernet, Token Ring, ARCNet and FDDI (Fiber Distributed Data Interface).
The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design. Later, Robert Metacalfe went to Xeros’s Palo Alto Research Center (PARC) laboratories and eliminated the radio portion and changed to co-axial cabling. Ethernet is one of the most popular LAN technologies in use today covering more than 85% of the networks. Ethernet system consists of three basic elements:
The physical medium use to carry Ethernet signals between computers on the network
A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium.
An Ethernet frame that consists of a standardized set of bits used to carry data over the system.
The operation of Ethernet can be described in simple terms as follows:
Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time.
To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity.
Modern Ethernet Network
As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.
What is Medium Access Control of Ethernet?
The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity, are called the “Medium Access Control” mechanism. The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMD/CD).
Explain Ethernet Frame.
The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact.
Advantages of Ethernet
Ethernet’s major advantages are:
It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s)
It is a proven technology that supports various writing configurations.
It works well with a large number of LAN and micro-to-mainframe applications.
It is easy to install.
What are the disadvantages of Ethernet Cabling?
The Ethernet cabling ahs the following disadvantages:
Ethernet is not a high-level performer in high-load environments. This protocol (CSMA/CD: Carrier Sense Multiple Access/Collision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk
Its linear bus cabling system can sometimes make it difficult to isolate problems.
ARC Net Board
The Attached Resource Computer Network (ARCNet) standard was created in 1977 at the Data Point Corporation by a scientist – John Murphy. ARCNet uses the token-passing protocol over a star and bus topology. The star and bus topology combines the flexibility of a star with the simplicity and throughput of a bus. Thus, ARCNet standard has a unique protocol/topology combination: token-passing protocol and Distributed star/bus topology.
Advantages of ARCNet
Here are some of the ARCNet’s advantages:
It is extremely reliable.
ARCNet is easy to install and troubleshoot.
It has an excellent track record of interoperability for those using ARCNet components from various manufacturers.
ARCNet supports a variety of cable types including coaxial, UTP and Fiber Optics.
It is inexpensive and built to stay that way.
Disadvantages of ARCNet
Here are some disadvantages of ARCNet:
Standard ARCNet is very slow (2.5 Mb/s). It is almost seven times slower than Token Ring.
ARCNet was not designed with interconnectivity in mind. For many installations, it’s difficult to go beyond the confines of single LAN.
The token-passing protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.
Logical Ring Physical Star topology for Token-Passing Standard
It is sure that any break in the ring at any point will interrupt communications for all machines. To solve this problem, IBM developed a modified ring topology, which they called the logical ring physical star. The central point of the physical star configuration is Token Ring hub called the multi-station access unit (MSAU, pronounced as masow). Workstations and servers attached to the MSAU through special STP adapter cables. IBM converted stars into a logical ring by connecting all MSAU hubs together through special ring-in (RI) and ring-out (RO) ports.
Network with MASU
Advantages of Token Ring
Here are Token ring’s most useful advantages:
It offers excellent throughput under high-load conditions.
Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM’s broader connectivity strategies.
It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling.
It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s).
Point out the disadvantages of Token Ring.
Few of the disadvantages of Token Ring are:
Token Ring is very expensive. All topology components cost much more than other more popular standards.
It is relatively proprietary. Token Ring’s complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it.
Engineers must have considerable expertise to manage and troubleshoot token ring components.
Beaconing and Auto-Reconfiguration
When a station does not receive a message from its nearest active upstream neighbor, it sends out a warning, otherwise known as a beacon. This beacon alerts everyone that something is wrong and helps to isolate the failure domain. When beacon occurs, the ring will attempt to fix the problem without your intervention. This process of self-healing is called auto-reconfiguration.
When two or more computer are connected with one another for the purpose of communicating data electronically, besides physical connection of computers, communication devices and system servers, a well defined standard known as architecture is required to establish cohesive communication between devices in Network.
Popular Network Architectures
The most popular architectures are:
ISO Open System Architecture (OSI)
IBM’s System Network Architecture (SNA)
ISO’s OSI Architecture
The Open System Interconnection (OSI) is a standard reference model for communication between two end users in a network. It is used in developing products and understanding networks which means commonly used Internet product and services fit within the model. The OSI model describes seven layers of related functions that needed at each end, when a message is sent from one party to another party in a network. Each layer has its own set of special related function as follows:
ISO’s OSI Architecture
Layer 7 – Application Layer: Application programs that use the network.
Layer 6 – Presentation Layer: Standardize data presented to the application.
Layer 5 – Session Layer: Manages sessions between applications
Layer 4 – Transport Layer: Provides error detection and correction
Layer 3 – Network Layer: Provides data delivery across the physical connection
Layer 2 – Data Link Layer: Provides data delivery across the physical connection
Layer 1 – Physical Layer: Defines the physical network media.
IBM’s SNA Architecture
OSI and SNA Comparision
SNA is a computer networking architecture that was developed by IBM to provide a network structure for IBM mainframe, midrange, and personal computer systems. SNA defines a set of proprietary communication protocols and message formats for the exchange and management of data on IBM host networks.
SNA can be used for the following types of tasks:
Terminal access to mainframe and midrange computer applications.
File transfer of data between computer systems.
Printing of mainframe and midrange data on SNA printers.
Program-to-program communications that allow applications to exchange data over the network.
SNA can be implemented in a networking infrastructure that uses either a hierarchical or peer-to-peer model.
Peer-to-Peer Networking Model
A networking model where each workstation has equivalent capabilities and responsibilities is known as peer-to-peer model. There is no central server in this network and computers join hands to share files, printers and Internet access. It is practical for workgroups of a dozen or less computers making it common environments, where each PC acts as an independent workstation that stores data on its own disk but which can share it with all other PCs on the network. Software for peer-to-peer network is included with most modern desktop operating systems such as Windows and Mac OS.
Client/Server Networking Model
A networking model where one or more powerful computers (servers) provide the different network services and all other user’s computers (clients) access those services to perform user’s tasks is known as client/server networking model. Client-server networking model became popular in the late 1980s and early 1990s as many applications were migrated from centralized minicomputers and mainframes to networks of persona computers. The design of applications for a distributed computing environment required that they effetely be divided into two parts: client (front end) and server (back end). The network model on which they were implemented mirrored this client-server model with a user’s PC (the client) typically acting as the requesting machine and a more powerful server machine to which it was connected via either a LAN or a WAN acting as the supplying machine. It requires special networking operating system. It provides user level security and it is more expensive.
Network and Internet Terminologies
Network interface cards, commonly referred to as NICs are used to connect a PC to a network. The NIC provides a physical connection between the networking medium and the computers’ internal bus, and is responsible for facilitating an “access method” to the network. Most NICs are designed for a particular type of network, protocol and media, although some can serve multiple networks.
LAN Card or NIC
Hubs/Repeaters are used to connect together two or more network segments of any media type. In larger design, signal quality begins to deteriorate as segment exceeds their maximum length. A hub provides the signal amplification required to allow a segment to be extended a greater distance. Passive hub simply forwards any data packets they receive over one port from one workstation to all their remaining ports.Active hubs, also sometimes referred to as “multiport repeaters”, regenerate the data bits in order to maintain a strong signal.
The bridge function is to connect separate homogeneous networks. Bridges map the Ethernet address of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are different, then the packet is “forwarded” to the correct segment. Bridges are also called “store-and-forward” device because they look at the whole Ethernet packet before making filtering or forwarding decisions.
Routing achieved commercially popularity in the mid – 1980s – at a time when large-scale Internetworking began to replace the fairly simple, homogeneous environments. Routing is the act of moving information across an Internetwork from a source to a destination. It is often contrasted with bridging, which perform a similar function. Routers use information within each packet to route it from one LAN to another, and communicate with each other and share information that allows them to determine the best route through a complex network of many LANs.
LAN switches are an expansion of the concept in LAN bridging, which controls data flow, handles transmission errors, provides physical addressing, and manages access to the physical medium. Switches provide these functions by using various link-layer protocols. LAN switches can link four, six, ten or more networks together. A store-and-forward switch, on the other hand, accepts and analyses the entire packet before forwarding it to its destination.
Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BaseT or 10Base2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver.
A Gateway is a device such as a mini or microcomputer capable of operating on a standalone basis but which also provides connection for communication with the other computers and access to shared resources.
Also called a proxy or application level gateway. It is an application that breaks the connection between sender and receiver. Thus, it helps us to prevent hacker from obtaining Internet address and detail of a private network.
Firewall is a method for keeping a network secure. It is mostly used in giving users access to the Internet in a secure fashion as well as to separate a company’s public web server from its internal network.
A node is a hardware device or group of devices or station in a network that link one or more other unit to the network.
The most and latest wireless LANs use electromagnetic airwaves either infrared or radio frequency to communicate information from one point to another without relaying on a physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies.
In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an Access Point (AP), connects to the wired network from a fixed location using standard Ethernet cable. The Access Point receives, buffers, and transmits data between the WLAN and the wired network infrastructures. A single Access Point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The Access Point (or the antenna attached to the Access Point) is usually mounted high but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained. The wireless network, printers or other peripherals can be shared through a connected PC. The devices then communicate using a set of reserved high-frequency radio waves. An Access Point device connects to a DSL or cable modem and enables high-rate (broadband) Internet access for the entire network.
Internet is the large worldwide network of computes that facilitates data communication services, file transfer, electronic mail, World Wide Web and newsgroup with common protocols.
Tim Berners Lee
The WWW is the brainchild of Tim Berners Lee a CERN who had the idea of creating an electronic web of research information. The web is currently the fastest growing Internet information system, with new resources being added regularly. The web relies on a set of protocols, conventions and software to operate. The web is a distributed system of delivering linked documents over the Internet. It is called a distributed system because information can reside on different computers around the world. Yet be easily linked together using hypertext. The web uses hypertext to create links from together using hypertext. The web uses hyperte3xt to create links from one resource to another. A hypertext link is usually displayed by highlighted and underlined text on the page. A hypertext link or hyperlink can also be graphic that acts as a button linking to another resource.
Internet Relay Chat (IRC) is a system for sending public and private message to other users in “real time” – that is, your message appears on the recipient’s screen as soon as you type it.
CU-SeeMe is a video conferencing system that allows users to send and receive sound and pictures simultaneously over the Internet.
It is a protocol or set of rules that enables a computer to connect another computer in network. It is also known as a remote login. The telnet operates on client-server principle.
The ghoper is a protocol designed to search, retrieve and display documents from remote sites on the Internet. The Ghoper was created as a piece of software to utilize some of the services that were becoming available on the Internet.
HTML stands for Hyper Text Markup Language. It is a standard coding language used to create all web documents (pages).
Different Browsers Logo
A browser is the Internet Client software that acts as an interface between the user and the inner-workings of the Internet, specifically the WWW. We can find graphical web browser that displays multimedia content of text, graphics, audio and video, and text web browser that displays only text. Internet Explorer, Netscape, Firefox are graphical web browser and Lynx is a well known text browser.
Dialup connection is a means of connecting user to another computer (ISP) or a network such as the Internet with a modem equipped computer.
IP Address is an identifier for particular machine on a particular network. It is part of scheme to identify computers on the Internet. IP addresses are a set of numbers separated with periods.
IP Address Structure
IP Address and Subnet Mask
A domain name is a way to identify and locate computers connected to the Internet. This is a text name of a computer in network or Internet. Domain names are converted to IP Addresses to locate computers and resources.
URL stands for Uniform Resource Locator that identifies a particular Internet resource. URL help the user to locate web page, gopher service, library catalog and image or text file locations. URLs are the standard addressing system of the www. A complete URL provides the web client with all the information it needs to contact a server and make a request for information. URLs are divided into three basic parts:
Protocol (http://) – The information appearing before the colon in any URL indicates the type of information server or protocol. For example http:// indicates that the server to be connected is a www server.
Domain name (www.psexam.com) – The second piece of information is the address of the server. In this example psexam.com is the name of the machine at PS Exam in world wide web.
Resource name (download.htm) – The third piece of information is the path to the actual document requested. In this example the URL indicates that the document in the system directory and is named download.htm.
Web Browsing or Surfing
Browsing or Surfing is the process of visiting different web sites on the Internet hosted by various organizations.
The search engine is an interactive tool to help people locate information via the www and it is interface between the user and underlying database. The most popular search engines are Alta Vista Exite, Lycos, Yahoo!, Google, Ask etc.
Meta Search Engine
A web meta searcher is a tool that helps users to locate information available via the World Wide Web. Web meta-serchers provide a single interface that enables users to search many different search engines, indexes and databases simultaneously. Some meta search engines are Albany.net, Clnet (search.com), Cyberland, Eureaka!, Savvysearch and so on.
We can access to the Internet in one of two basic ways, dialing into an Internet Service Provider’s (ISP) computer or with a direct connection to an ISP. Connecting to ISP by dialing their hunting number (phone number) is called Dial-up connection. We require a username, password and ISP’s hunting number to configure Dial up Connection.
An Extranet is a type of Intranet (Internal TCP/IP Network) that has been selectively opened to a firm’s suppliers, customers.
An intranet can be defined as a network connecting an affiliated set of clients using standard internet protocols, esp. TCP/IP and HTTP or as an IP-based network of nodes behind a firewall, or behind several firewall connected by secure, possibly virtual, networks.
A web index is designed to assist users in locating information on the World Wide Web. Web indexes are also referred to as catalogs or directories. A web index collects and organizes resources available via the www. Some of the web indexes are Yahoo!, Megallan, Apollo etc.
The hypertext allows for the integration of text, graphics, audio and video on a web pate. This can make it very easy to browse and very exciting to view. A web page may have colorful graphics integrated with textual information. Links on a web page may take you to other web pages, recorded sonds, or digital video clips. A single click on any hyperlink allows you to follow the link to the specified resource.
Hypertext and Hyper Link
Electronic Mail (Email) is one of the most popular & powerful communication tools on the Internet. It is an efficient and effective means of network communication. Email allows you to communicate with people across the globe via electronic media (computer).
An Email Address identifies a person and the computer for the purpose of exchanging electronic mail message.
The email address contains three parts:
Username – The admin in example.
Domain name of organization – The psexam in example
Top Level Domain – The com in example
It is an element of Email Application which collects all incoming mails.
It is an element of Email Application which collects all outgoing mails, if it is created and sent in offline.
This is an element of Email Application that holds all the deleted emails.
CC stands for Courtesy copy or Carbon Copy. It is an element of Email used to specify the additional recipients when the mail sent needs to be acknowledged to them.
BCC stands for Blank Carbon Copy. It is similar to CC but the address of other receivers will not be shown to the receiver.
A reply is the response of an email you receive. After you read a mail and need to reply it you can use this feature.
A mail received can be sent to be other recipients known as forwarding.
The documents created in other applications such as word, excel can be sent along with the email message. These documents that are sent with email is known as attachment. Documents, audio/video files, Zip files etc. can be sent as attachment along with email message.
When a mail sent can’t reach to destination and returns back, this is known as bounced. This happens often when the recipient’s address is wrong or the server at the recipient’s end is down or recipient’s inbox is full.
It is essential for all users on the internet to recognize that they are responsible for their own individual actions while using the net. Netiquette is simply the use of common courtesy and polite behavior while using the net.
The convention of expressing feeling or a joke in symbolic form by user in Email or Chatting for example for smiling for winking for frowning etc are emoticons.
Points to Remember
Computer network is an interconnected collection of autonomous computers. In simple words, computer network is a group of computers and other devices interconnected by communication channels that facilitates communication, sharing devices and other resources.
To create a network you need computers equipped with network interface cards (NIC), transmission media such as cable, connection devices such as switches, routers etc and network software (NOS and communication software).
Benefits of networking – quick and efficient data transfer, sharing resources, saving money on software, access to information in remote computer, high reliability of services, workgroup computing.
Drawbacks of networking – network systems are more sophisticated and complex to operate; when network service become unstable the productivity fails; proper maintenance of network computer require considerable time and expertise; file security is more important if connected to network; spreading of malicious viruses is more probable in networked environment.
Computer network consists of hardware components ( servers and/or clients, connectors, network cables, network interface cards, switches, gateway, routers) and Software components (network operating systems, network protocols such as TCP/IP, HTTP, SMTP, POP and so on)
Network Operating System is a system software that controls other software and hardware than runs on a network. It provides services such as printer sharing, common file system and database sharing, application sharing and other housekeeping tasks of a network.
Windows Server 2003, Windows Server 2008, Unix, Netware etc are examples of NOS (Network Operating Systems).
Network Protocol is the set of rules that govern the transmission of data over network. This is a formal description of messages formats and the rules that two or more machines must follow to exchange those messages.
TCP/IP (Transmission Control Protocol / Internet Protocol) is a basic communication protocol. TCP/IP is a two layer protocol. The higher layer TCP manages the assembling of a message or file into smaller packets that can be transmitted over the Internet. It again reassembles the packets into original message at the receiving end. The lower layer IP handles the address part of each packet so that it gets to the right destination.
HTTP (Hyper Text Transfer Protocol) is the protocol for transferring files (text, graphics, images, sound, video and other multimedia files). The primary function of HTTP is to establish connection with the server and send HTML pages back to the user’s browser. It is also used to download other files in browser or other applications.
SMTP (Simple Mail Transfer Protocol) is the protocol used to send email message across the Internet.
Post Office Protocol (POP) is the protocol used to retrieve email messages from server to client’s email applications such as Eudora, Microsoft Outlook and so on. Most of the modern browser such as Internet Explorer, Netscape, Firefox, Chrome contains built-in POP in them.
5 Network services – File service, print service, message service, application service and database service.
File service in network provides file transfer, storage, data migration, file update synchronization etc.
Print service in network offers printer sharing. It includes accepting print job request, interpret print job formats, printer formats, configuration, manage queues and interact with networkable printers and faxes.
Message service in network allows the users to pass on the message from one computer to other computers. Message service functions are email, voice mail and object orientation applications.
Application service are the services that run software for network clients and allow computers to share processing power.
Database service provides centralized data storage and retrieval to network clients.
3 Computer Network Models – Centralized computing or hierarchical networking, client/server network, peer-to-peer network.
Centralized computing network is also called host based network where there is a central host computer which offer information, resources, services and applications to the users or other nodes of network. This network is expensive to implement.
Client/Server network contains one or more server computer that provide network services to other computers that are known as clients. Client/Server network model is the workhorse of the network world.
Peer-to-peer network also called workgroup is a server less network model where each computers are independent and equal in terms of providing and using network services. This model is completely decentralized network mode. Though they are easy and inexpensive to implement, they are suitable only for small organizations.
Networks can be classified into 3 types based on geographical spread – LAN, MAN and WAN.
Local Area Network (LAN) is a small network connecting two to several hundred computers withing local area such as single building or company complex. The computers are connected with network cable or short-range wireless technology.
Wireless LAN or WLAN connects devices and computers over a short distance with wireless technology that uses radio waves. NIC cards that support wireless connections have small antenna on it. Data signals transmitted by these antenna are picked up and routed by a wireless network switch known asAccess Point.
A wireless technology known as Wi-Fi (Wireless Fidelity) is used for setting up high speed WLANs over a distance up to 30 meters.
Metropolitan Are Network (MAN) is a medium sized network that spans over a metropolitan network. MAN typically use wireless infrastructure or optical fiber connections. Cable TV network is a good example of MAN.
Wireless MAN or WMAN is a type of wireless network that connects several wireless LANs over a city. A wireless technology WiMAX (Wireless Interoperability for Microwave Access) is used for setting up wireless MANs within a radius of 50 km.
WAN (Wide Area Network) is the largest network that spans over different countries or whole world. WAN uses different technologies for connection such as long distaance telephone, wires, microwaves and satellites. The Internet is an example of WAN.
Network Topology is network structure that tells how nodes are connected to form the network. Physical topology is the actual geometric layout of nodes. The basic typologies are Bus, Star and Ring. You can create other topologies like mesh, hybrid, tree topologies by combining and modifying the basic typologies.
The choice of topology for a network will depend upon the choice of transmission media, access method, desired performance, reliability, size, expandability, cost, availability of communication lines etc.
Bus topology is one of the basic topology where nodes (computers and/or network devices) are connected linearly, with each node directly connected to the network cable (known as trunk or bus). A drop cable is connected with the trunk using a T connector. The bus has terminator at both end which absorb the signal to remove it from bus if it is not picked by any node.
Bus topology is easy to implement and extend, easier to identify the cable fault but this topology has disadvantages like limited cable length and number of stations, the problem in network cable (trunk or bus) causes the break down of entire network, and the maintenance cost can be higher in long run.
Ring topology is a network structure where arrangement of nodes forms a loop or ring. The data is sent to only one direction of the ring and each node picks up, checks if it is destined to it, if not re-transmits down to the next neighbor. So the signal quality in ring topology is high. Any data packet if returned to the sender, the sender removes it from ring.
Ring topology performs better under heavy network load than bus topology, does not require network server and it is easier to use optical fibers as transmission media but ring topology has disadvantageslike node failure causes network failure, it is difficult to diagnose faults in ring topology, network configuration is difficult.
In Star topology, there is a central computer or network device like hub, switch etc. with which all other nodes are connected (all-to-one connection). The central computer is called hub node and other computers are leaf nodes. All the data passes through the hub node to reach up to its destination. Hub manages and controls all the functions as well as acts as a repeater for the data flow.
Star topology has advantages such as it is easy to install, detect faults and remove parts, no disruptions to the network functioning when adding new nodes or removing nodes. However star topology suffers from drawbacks like heavy dependence on hub node and problem in hub node can cause whole network failure, the performance and scalibility (extendability) of network depends on the capability of hub.
A data packet is a basic unit of communication over a digital network. A packet is also called adatagram, a segment, a block, a cell or a frame depending on the protocol. When data has to be retransmitted, it is broken down into similar structure of data packet, which are reassembled to the oritinal data chunk once they reach their destination.
Hub, repeater, switch, bridge, access points, router, gateway are the network connection devices.
Hub is a small simple inexpensive device that connects multiple computers together. Hub receives the incoming data packet, amplifies it and broadcasts them to all the LAN cards in a network. The destined recipient receives the data packet and all others discard it.
Passive hub simply joins wires from several station and does not provide any processing or regeneration of signals.
Active hub in a network can regenerate signals on the output side to keep the signal strong.
Intelligent hub can perform a variety of processing functions including network management, bridging, routing and switching. Switch, bridge and router are intelligent hub.
Network repeater is a connection device that amplifies and restores signals for long distance transmission. Repeaters are often used in trans-continental and submarine communication cables because the signal loss over such distances would be unacceptable without them. There are repeaters for copper wires and fiber optics.
Network switch is a network connection device that is used to segment networks into different subnetworks called subnets or LAN segments. It helps to prevent traffic overloading in a network.
Network bridge is a network device that establishes an intelligent connection between two local networks with the same standard. In simpler words, it is a connection device to connect two or more LANs having similar systems.
Wireless access point is a device to connect wireless devices and can connect to wired networks. They have network interface to connect to the wired network and an antenna or infrared receiver necessary to receive the wireless signals.
Router is a network device that connects multiple networks that use the same protocol. Routers can detect the best rout to forward data packet.
Gateway is a network device that can connect disimilar networks with different protocols. They can transmit data between different operating systems, different email formats or between totally different networks. Gateway are commonly used to transfer data between private network and the Internet.
MODEM (Modulator and Demodulator) is a network connection device that performs the modulation and demodulation function. It is required to connect a computer with network through telephone lines.
Modulation is the process of converting computer generated digital data into analog signals so that they can be transmitted through telephone lines.
Demodulation is the process of converting analog signal from telephone lines into digital data so that the computer can do further processing.
The data transfer rate in MODEM is usually measured in bits per second (bps). The unit kbps is kilo bits per second. Similarly KBps represent kilo bytes per second.
A communication Channel (communication link or line) forms the path over which data travels as it passes from a sending device to a receiving device in a telecommunications system. It is composed of one or more transmission media
Transmission media refers to the mode of connection needed for data transmission. There are two types of communication media – guided (bound) and unguided (unbound) transmission media.
Guided media are the bound transmission media in which data/signal is guided by the cable or wire. Because these media are limited by physical geography, they are also called bound transmission media. All the transmission cables fall under this category. Some examples are twisted pair cables, co-axial cables, fiber optics cable etc.
Twisted pair cables are the oldest and still most common medium of transmission. It consists of pairs or wires twisted with each other. The wires are twisted so as to reduce the EMI (Electro-Magnetic Interference) effect – the disturbance in signal flow due to the electronic or magnetic field.
UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair) are the two types of twisted pair cables.
UTP are the most common transmission media for LAN networking. It does not include shielding around its conductors. UTP can support the distance up to 100 meters and data transfer speed of 1 Gbps.
STP include shielding typically a foil wrapper around its conductors to improve the resistance against interference and signal noise. It is more expensive than UTP and supports the distance up to 90 meters.
Co-axial cable was invented by Oliver Heaviside – an English engineer and mathematician in 1880.
Co-axial cable consists of a central inner conductor surrounded by a flexible insulating layer which is again surrounded by fibers of conductor. The term co-axial comes from the inner conductor and the outer shield sharing the same geometric axis.
Co-axial cables are popularly used for cable television signals, computer network connection and connecting radio transmitters and receivers with their antennas.
Fiber optics is the transmission medium where photons – the pulses of light – flows rather than electrons as in twisted pair cable or co-axial cables.
Fiber optic cable consists of (i) core – the glass or plastic tube through which the light travels, (ii) cladding – the covering of the core that reflects light back to the core, and (iii) the protective coating – which protects the cable from hostile environment.
Fiber optics can easily carry data at more than billion bps. Fiber optics is not affected by magnetic fields or electronic fields – so free from EMI.
Unguided media are the unbound transmission media in which data or signal is sent through the air instead of cables. It includes wireless transmission methods such as radio networking (radio wave), infrared, microwave and infrared.
In Radio Networking, signals are sent through radio frequency (RF) waves in the 10 KHz and 1 GHz.
Radio wave is affected by electrical interference from power lines, buildings, hills and atmospheric conditions.
Baseband and broadband are teh two types of radio used in networking. Baseband uses carrier’s entire bandwidth to send a single data stream while broadband sends multiple signals on the carrier at the same time.
Radio transmission was invented by Nikola Tesla in 1893.
Bueetooth is an open wireless technology standard for exchanging data over short distance using short wavelength radio transmission. Bluetooth can be used to create PAN (Personal Area Network).
Bluetooth was invented by Ericsson company in 1994.
Infrared is an unbound transmission media in which signals are sent via pulses of infrared light. Infrared communication is possible only on LOS (Line of Sight).
Microwave transmission involves the sending and receiving data using microwave signals over a microwave link. This link is made up of microwave radio antennas located at the top of towers. Because there should not be any obstruction between the microwave antennas and microwave is transmitted in straight line, the towers are often built on the top of building or hills.
Microwave is commonly used for communication system on the surface, in satellite communication and in deep space radio communication.
There are 3 different transmission mode – simplex, half-duplex and full duplex.
Simplex is one way communication mode where one device only sends the data or signals and other devices only receive. Radio, television are the examples of simplex transmission mode.
Half-duplex is two way communication mode but only one at a time. Walki-talkie operates in half duplex mode.
Full duplex is the transmission mode where data is transmitted in both the directions simultaneously on the same channel. Telephone is an example of full duplex mode.
Bandwidth is the term used to describe how much information can be transmitted over a connection in certain time. It is the measurement of the capacity of a communication signal. For digital signals, the bandwidth is the data speed or rate which is measured in bps (bits per second) or some larger denominations such as kbps (kilo bits per second), mbps (mega bits per second) and so on. For analog signals, bandwidth is the difference between the highest and lowest frequency components which is measured in hertz (Hz).
There are 3 bandwidths for communication channels – narrow-band, voice-band and broadband channel.
Narrowband transmit data at a rate between 40 to 100 bps. It is used where the data volume is relatively low. Telegraph lines are example of narrowband channel.
Voiceband channel transmit data at a rate between 110 to 9600 bps. It is used to handle moderate data. Standard telephone lines are the examples of voiceband channel.
Broadband is high speed, high capacity transmission medium that can carry signals from multiple independent network carriers. Broadband channel is established using co-axial or fiber optics cable. Broadband technology can be used to transmit data, voice and video over long distances simultaneously.
Data travels in 2 ways over transmission medium – serial data transmission and parallel data transmission
In serial data transmission, bits flow in a series or continuous stream. The cost of communication hardware is considerably reduced because only a single wire or channel is required for teh serial bit transmission. Telephone lines use serial transmission.
In parallel data transmission, bits flow through separate lines simultaneously. It is a standard method of sending data from computer CPU to printer. Parallel transmission is suitable only for short distance and not used over telephone lines.
Data transmission mode can be Asynchronous or Synchronous
In asynchronous transmission data is sent and received one byte at a time. It is often used with microcomputers for terminals with slow speeds.
In synchronous transmission greater quantities of information is sent by sending several bytes or a block at a time. For synchronous transmission, blocks of bytes must occur at carefully timed intervals.
The Internet is a global, public wide area network (WAN) that provides internet services such as WWW, email,FTP, IRC, Usenet, Newsgroup, video conferences, e-commerce, e-learning and so on.
The Internet originated from an experimental network called ARPANET created in 1969 by the U.S. Department of defence’s Advanced Research Projects Agency.
ARPANET was later replaced by NSFnet which was run by National Science Foundation which permitted universities and research agencies to link up with its supercomputers.
Ultimately, many private networks get connected with ARPANET and NSFnet to form the Internet. The Internet became publicly opened since 1990.
To set up internet you need a computer, a modem and telephone line. You need to install necessary software such as TCP/IP, browser and email client. Finally you should get a connection to ISP who provide you the username and password to connect to the Internet.
A dial-up connection is a temporary connection set up between your computer and ISP server through telephone lines.
Broadband internet connection is a high bandwidth connection to the Internet which is easier and faster to use than the traditional dial-up networking. Broadband can be provided through telephone line (ADSL), via cable or via satellite or via other wireless technologies such as Wi-Fi, WiMAX.
Email is one of the most important service of Internet. It is used to exchange messages like in traditional mails. Email uses popular protocols SMTP for sending emails and POP to receive emails.
WWW (World Wide Web) is the most popular service of Internet which provides webpages. It was created by Tim Berners Lee in 1991. The web gives users access to a vast array of documents that are connected to each other by means of hyperlinks.
Search Engines are very useful Internet service that helps you to find web pages, people and other resources in the Internet. Google, Yahoo, Bing are some of the popular search engines.
FTP (File Transfer Protocol) is another service in the Internet that lets you send and receive files over the Internet. The process of transferring a file from remote computer (servers) to your local computer is known as downloading and the reverse is uploading.
IRC (Internet Relay Chat) or web chat is a service in the Internet that lets you exchange instant messages. It is popularly called chatting.
Video conference or video teleconference is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmission simultaneously. People on those locations can talk to each other as in conference. For video conference you need a computer equipped with microphone, webcam, broadband internet connection.
Usenet Newsgroups are worldwide discussion groups in which people share information and ideas on a particular topic. Discussion takes place in electronic bulletin board and the topic can range from personal problems to anything that can be discussed.
Remote Login is one of the earliest Internet service that lets you to log in to a remote computer and use its service and resources.
eCommerce refers to the buying and selling of goods and services on the Internet, especially the WWW. Companies set up their websites through which customers can buy the products and pay through online payment methods such as credit cards, PayPal and so on.
E-Learning is the use of technology to enable people to learn anything at anytime and from anywhere. Because of the development of the Internet, the distance learning has become possible and virtual classes help students to attend class from different part of world.
Web servers are the server computers and software in the Internet that offers different internet services. It receives the requests from clients, fetches the resource and sends it to the client computers. Apache, IIS are some examples of web server applications.
Web browsers are the client applications in users’ computers that send request to the web servers and display the web pages when server returns the request. Mozilla Firefox, Google Chrome, Internet Explorer are some examples of web browsers.
Web Page is a HTML document or resource of information that is suitable for the WWW and can be accessed through a web browser and displayed on a monitor or mobile device. Web pages are requested by browsers and sent by servers using HTTP protocol.
Website is a collection of web pages containing text, images, audio and video files.
Homepage is the opening page or main page of a website intended to greet the user, provide information and offer navigation to other pages in website. The filename of homepage is usually ‘default’ or ‘index’.
Uniform Resource Locator (URL) is the address of web page, images or any other content resource. You can open any content of Internet by typing its URL on address bar of browser. For example http://icttrends.com/ecourse/session-13.htm is a URL to open Session 13 page of eCourse in ICT Trends.
Domain Name System (DNS) is a technology in the Internet to convert Domain Names into IP address and vice versa.
A domain name is a name chosen for a website in internet or a computer in network.
HTTP (Hyper Text Transfer Protocol) is a protocol used by world wide web to establish client and server interaction. HTTP protocol is used to transfer webpages over internet.
Intranet is a private network within an organization that uses the standards and protocols of Internet. It is used to provide interaction, communication and information to their employees.
Extranet is a private network that uses the internet technology and the public telecommunication system to connect more than one organization. Many organizations use Internet technologies to allow suppliers and other limited access to their networks.
Numbering systems are, in fact, pure mathematics. And because computers are computing devices, learning mathematics makes you more efficient to understand and use computers.
Number systems are an organized and systematic way of representing numbers. Each numbering system has its own set of symbols and a set of rules to determine how a quantity is represented and how operations can be performed. For example Roman Number System has symbols like I, II, III, IV, V, …. and Hindu Arabic System (Decimal) has symbols like १, २, ३, ४, ५…. or 1, 2, 3, 4, 5….
A numbering system is positional if the position of a number matters the value it represents. For example in 002000 and 000020 the value ‘2’ represents is different because it is on different positions in those two numbers. In first number the 2 represents 2 * 10 ^ 3 (2 into 10 to the power 3) = 2000 whereas in second number 2 represents 2 * 10 ^ 1 (2 into 10 to the power 1) = 20.
A numbering system is non-positional if each symbol represents same value regardless of its position. Roman numbering system is an example of non positional numbering system.
Among these numbering systems, we are more concerned with positional numbering systems.
There are different number systems in positional systems based on how many symbols it has. Such as:
2 different symbols – 0 & 1
Quinary – 5 differnt symbols – 0, 1, 2, 3 and 4
Octal – 8 different symbols – 0, 1, 2, 3, 4, 5, 6 and 7
Decimal – 10 different symbols – 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9
Hexadecimal – 16 different symbols – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F
The value a number in any system represents is the product of the sum of its digits and its positional value. for example:
1 * 2 ^ 3 + 1 * 2 ^ 2 + 0 * 2 ^ 1 + 1 * 2 ^ 0 = 8 + 4 + 0 + 1 = 13
2 * 5 ^ 3 + 0 * 5 ^ 2 + 3 * 5 ^ 1 + 1 * 5 ^ 0 = 250 + 0 + 15 + 1 = 266
1 * 8 ^ 3 + 3 * 8 ^ 2 + 6 * 8 ^ 1 + 0 * 8 ^ 0 = 512 + 192 + 48 + 0 = 752
8 * 10 ^ 3 + 3 * 10 ^ 2 + 1 * 10 ^ 1 + 6 * 10 ^ 0 = 8000 + 300 + 10 + 6 = 8316
3 * 16 ^ 3 + A * 16 ^ 2 + 2 * 16 ^ 1 + F * 16 ^ 0 = 12288 + 2560 + 32 + 15 = 14895
In above example, the numbers in red color are place value. * is used as multiplication sign and ^ as raised power.
For our computer operator and similar jobs examination, we need to learn how to convert a number expressed in one system into another (conversion) and perform binary addition, subtraction, multiplication and division of binary numbers (operations). Among these, you already learned one method!
Converting numbers from any system into decimal numbering systems
No mater in which numbering system the given number is, you can get the decimal equivalent by
multiply each digit by its face value
2) add all the products.
In above examples, we have converted binary 1101 into decimal 13; quinary 2031 into decimal 267; octal 1360 into decimal 752 and hex 3A2F into decimal 14895.
Converting decimal numbers into any other systems
To convert given decimal into any other required system, you will perform the following action
Divide the number by the base of new system succesively (integer division – no
2) Note down the remainders in reverse order
a) Convert 74 into binary.
74 / 2 = 37 remainder 0
37 / 2 = 18 remainder 1
18 / 2 = 9 remainder 0
9 / 2 = 4 remainder 1
4 / 2 = 2 remainder 0
2 / 2 = 1 remainder 0
1 / 1 = 0 remainder 1
Collect remainder in reverse order (bottom to top)
= binary 1001010
Convert 379 into octal
379 / 8 = 47 remainder 3
47 / 8 = 5 remainder 7
5 / 8 = 0 remainder 5
remainder in reverse order
= octal 573
Convert 984 into Hexadecimal
984 / 16 = 61 remainder 8
61 / 16 = 3 remainder 13 (i.e. D)
3 / 16 = 0 remainder 3
remainder in reverse order
= octal 3D8
Quick method to convert decimal into binary
You can find the binary equivalent of a decimal number by
1) break the number into the sum of different powers of 2
-> 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, …. are the numbers that can
be raised power of 2
Powers of 2 -> 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
2) note down the presence and absense of positions
Convert 1568 into binary
Break the number. The closest number to 1568 that can be raised power of 2 is 1024 (i.e. 2^10)
= 1024 +
544 [Again, the closesest number to 544 is 512 (i.e. 2^9)]
= 1024 + 512 + 32 [Again, the closest number to 31 is 16 (i.e. 2^4)]
= 1024 + 512 + 32
= 2 ^ 10 + 2^9 + 2^5
You don’t need to show all the procedure as above. Just write the closest number and then write closest of the remainder and so on. Finally when you get the sequence of numbers like below, the job is almost done!
= 1024 + 512 + 32
Power of 2 of above numbers = 10 + 9 + 5
Now, write 1 for all the positions that are present and 0 for the positions that are absent. In above example, position 10,9 and 5 are present other positions are absent. So the binary number will be:
Therefore binary 11000100000 is equivalent to 1567.
If you practice for some time with your mind-work, you’ll be able to convert into binary very quickly. All you need to remember is the numbers that can be raised power of 2.
Binary number into Octal
Any number given in Binary can be very easily converted into Octal numbering system
1. Create groups from right most with 3 bits
2. Convert each group into binary
10110100110 into octal
Solution: Grouping 10 110 100 110
Convert each group 2 6 4 6
Therefore, 2646 in octal.
Octal number into binary
Any given octal number can be converted into binary by:
1. Convert each digit into binary.
2. Add leading zeros if there are not 3 bits for every digit
Convert octal 6125 into binary
Solution: convert each digit 6 1 2 5
110 1 10 101
Make 3 bits for each digit 110 001 010 101
Therefore, 110001010101 is binary equivalent.
Hex number into Binary
Converting hexadecimal number into binary is similar to that of octal to binary. Only the difference is the number of bits in each group. In case of hexadecimal, there should be 4 bits in each group.
Convert 3A2F into binary
Solution: Convert each digit
3 A (10) 2 F (15) [A is 10, B is 11, C is 12, D is 13, E is 14 and F is 15]
11 1010 10 1111
Make 4 bits for each conversion by adding leading zeros
0011 1010 0010 1111
Therefore, 11 1010 0010 1111 is the binary equivalent.
Binary into Hexadecimal
This is also similar to the binary into octal. Only remember that there should be 4 bits.
Solution: Grouping 4 bits from right 1011 1010 0100 0110
Convert each group 11 (B) 10(A) 4 6
Therefore, BA46 is hex equivalent.
Another type of question included in PSC Exam is binary operation – add, subtract, multiply and divide binary numbers.
Binary addition is fairly simple and fun to operate. Following is the rules related to binary addition:
1) 1 + 0
= 1 [pretty obvious, isn’t it?]
2) 0 + 1 = 1 [Addition is associative. a+b = b+a, so same result]
3) 0+0 = 0 [What’s new? this is what we are always doing!]
4) 1+1=10 [Here is what binary differs. In decimal system 1+1 = 2 and that 2 is 10 in binary. So it is fairly understandable.] While you perform addition, you will write 0 on the sum and take 1 as balance to add up to the sum of preceding digit.
Add 1011010 and 10110
1 0 1 1 0 1 0
1 0 1 1 0
1 1 1 0 0 0 0
Addition is done from the last digit. Because both digits are zero, so write 0 on the answer line.
On next digit (second last digit of both numbers), because both digits are 1, due to the rule #4 the sum is 10. So write 0 on the answer line and take 1 as balance.
For the third last digit, because given numbers are 0 and 1, their sum is 1 (rule #2). This sum 1 and our previous balance 1 have to be added makes 10. So write 0 on the answer line and take 1 as balance for next digit.
Now on fourth last digit we have 1 & 0. The sum is 1 and with the previous balance, updated sum is 10. Write 0 on the answer line and take 1 as balance for next digit.
On fifth last digit, we have 1 & 1 to add. Sum became 10. because we had previous balance 1 the updated sum is 11 (10+1 = 11). Write 1 on the answer line and take 1 as balance.
Because the second number does not have sixth last digit, 0 from the first number and previous balance 1 makes up the sum of 1. Write that 1 in answer line. Remember there is no balance on this step.
For the seventh last or the first digit of first number, we don’t have digit from second number and also we don’t have previous balance. Therefore, copy that digit 1 into the answer line.
Thus, finally, we have 1110000 as the sum of given two numbers.
Binary subtraction is as simple as that addition was. In addition, you just need to remember to adjust the balance, in case of binary subtraction, you’ll remember to adjust the carry over.
for subtraction is:
1) 0-0=0 [obvious!]
2) 1-0=1 [nothing different]
3) 1-1=0 [this is what we are always doing]
4) 0-1=1 with carry over 1 [Here is what binary operations comes]
Subtract 10011 from 10110101
1 0 1 1 0 1 0 1
1 0 0 1 1
1 0 1 0 0 0 1 0
Subtraction is done from last digit of the numbers. Because both the numbers has 1 on its last digit, the difference is 0 (1-1=0). Write that 0 on answer line.
On second last digit, you need to subtract 0-1. Because the difference is 1 with carry over 1, write difference 1 on answer line. Remember there is carry over.
On third last digit, because carry over 1 is there, subtract it from the 1 of first number. The adjusted difference is 0. From this 0 you need to subtract 0 of second number, because 0 – 0 = 0, write 0 on answer line. No carry over.
On fourth last digit, both digits are 0, so write 0 on answer line. No carry over.
On fifth last digit, both digits are 1. So, write 0 on answer line. No carry over.
Because there are no digits left on second number copy other digits in answer line.
Thus, we got 10100010 as the answer.
Binary multiplication is very similar to the decimal multiplication except when you are adding. The rules of binary multiplication is as follows:
1) 1 x 1
2) 1 x 0 = 0
3) 0 x 1 = 0
4) 0 x 0 = 0
Everything perfectly same, isn’t it? Let’s see an example.
Multiply 1011 by 110.
0 0 0 0
1 0 1 1
1 0 1 1
1 0 0 0 0 1 0
Binary division is easier than decimal division as there are only two possibilities, either it will won’t go or if it goes, it goes for 1 time.
Divide 110110 by 110
110 ) 110110
Therefore, 1001 is the quotient of division and nothing is remainder.
I hope I put forward the method of binary operations in a way that you can start practicing the operation. If you are still confused about numbering systems, conversion and operations, you can drop your question at
Explanation of the Keys on a Windows QWERTY Keyboard
Q W E R T Y
“The name “QWERTY” for our computer keyboard comes from the first six letters in the top alphabet row (the one just below the numbers). It is also referred to as the “Universal” keyboard. It was the work of inventor C. L. Sholes, who put together the prototypes of the first commercial typewriter in a Milwaukee machine shop back in the 1860’s.”
Equivalent to clicking the Cancel button. In PowerPoint the Esc key will stop a running slide show. On a web page with animations, the Esc key will stop the animations. On a web page that is loading, the Esc key will stop the page from loading. The keyboard combination Ctrl + Esc will open the Start Menu.
F1While working in an application, depressing this key will bring up the applications help menu. If there is no open application F1 will open Windows Help.
F2Choose this key to rename a selected item or object.
F3Depressing this key will display the Find: All Files dialog box.
F4Selects the Go To A Different Folder box and moves down the entries in the box (if the toolbar is active in Windows Explorer)
F5Refreshes the current window. In Internet Explorer, F5 will Refresh the web page.
F6Moves among panes in Windows Explorer.
F10Activates menu bar options. Use right and left arrows to select menus and down arrows to display pull down menus.
F11In Internet Explorer this key will allow you to google between full screen viewing mode and normal viewing mode.
Usually located at the upper right hand corner of your keyboard next to the Scroll Lock and Pause/Break keys. Often abbreviated PrtScr, thePrint Screen key is a useful key supported on most PCs. In DOS, pressing the Print Screen key causes the computer to send whatever images and text are currently on the display screen to the printer. Some graphics programs and Windows, use the Print Screen key to obtain Screen Captures.
This key can be used to move forward through options in a dialog box.
Ctrl + Shift + Tab can be used to move backward through the options.
Ctrl + Tab allows movement from one open window to the next in an application with more than one open window.
Alt + Tab displays a list of open application windows. Keeping Alt depressed and selecting Tab cycles through the list. Releasing selects the highlighted application window.
Locks the keyboard in “Capitals” mode (only applies to Alpha keys). The Caps Lock key should be used with caution. Using ALL CAPS is a usability no-no as many have difficulty scanning text that is ALL CAPS. Also, when sending email in ALL CAPS, THIS COULD BE MISCONSTRUED AS SHOUTING AT SOMEONE.
The obvious use of this key is to allow selection of capital letters when depressing the alphabet characters, or selecting the characters above other non-alpha keys.
Depressing the Shift key while inserting a CD-ROM will bypass auto play.
Shift + Delete to permanently delete a selected item, bypasses the Recycle Bin.
Depressing the Ctrl key while clicking allows multiple selections. Holding the Ctrl key down and pressing other key combinations will initiate quite a few actions. Some of the more common ones are listed below.
Select All items
Add or remove Bold formatting
Copy, places the selected/highlighted copy on the clipboard.
Ctrl +C +C
Opens the clipboard.
Opens the Find what: dialog box. Great for finding references on a web page while using your favorite web browser.
Replace, brings up the Find and Replace dialog box. Great for global find and replace routines while working in normal and html views in your favorite WYSIWYG editors like FrontPage. You can also use this to find and replace content within your Word Documents, Excel Spreadsheets, etc…
Add or remove Italic formatting.
Window, In Internet Explorer, opens a New Window. In Outlook, opens a New Mail Message. In most publishing programs like Word, opens aNew Document.
Open, brings up a browse dialog and allows you to select a file to open.
Add or remove Underline formatting.
Paste, inserts the copy on the clipboard into the area where your flashing cursor is positioned or the area you have selected/highlighted.
Close, will close the document currently open.
Cut, removes the selected/highlighted copy and places it on the clipboard.
Redo last command. Many software programs offer multiple Redo’s by pressing Ctrl + Y + Y + Y…
Undo last command. Many software programs offer multiple Undo’s by pressing Ctrl + Z + Z + Z…
Open the Start menu (or use the Windows Key if you have one).
Spell checker (pre WinXP).
While dragging a file to copy the file.
While dragging a file to create a shortcut.
Allows movement (toggle) from one open window to the next in an application with more than one open window.
Close a window in an application without closing the application.
In Internet Explorer, Ctrl + F5 will Refresh the web page bypassing cache (all images and external file references will be reloaded).
On either side of the spacebar, outside the Alt key, is a key with the Windows logo. Holding the Windows key down and pressing another key will initiate quite a few actions. Some of the more common are listed below.
Displays the Start Menu.
Minimizes all windows and shows the Desktop.
Opens all windows and takes you right back to where you were.
Opens a new Explorer Window. Probably one of the hottest Windows keyboard shortcuts. This one gets a lot of hoorahs!
Displays the Find all files dialog box.
Lock your Windows XP computer. Logoff in Windows Pre-XP.
Minimizes all open windows.
Restores all previously open windows to how they were before you Minimized them.
Displays the Run command.
Displays the WindowsHelp menu.
Displays the Systems Properties dialog box.
Cycle through the buttons on the Task Bar.
Located on either side of the space bar. Holding the Alt key down and pressing another key will initiate various actions. Some of the more common ones are listed below:
Closes the current active window. If there is no active window this opens the Shut Down dialog box.
Alt + underlined letter in menu
To carry out the corresponding command on the menu.
Alt + left/right arrows
In a browser moves forward or back through the pages visited in a window.
Alt +Space Bar
Displays the current window’s system menu. This is the same as left clicking on the application icon at the top left of the window.
Displays a selected items properties. This can also be done with Alt + double-click.
Captures the top window of the active application.
Alt +Space Bar
Displays the main window’s system menu. This is the same as clicking on the application icon at the left end of the title bar.
Alt +Space Bar +C
After the system menu is displayed (see above), this combination will close a window. This works the same way as Alt + F4 but requires less stretch.
Alt +– (hyphen)
Displays the current window’s system menu. This is the same as left clicking on the application icon at the top left of the window.
Displays a list of open application windows. Keeping Alt depressed and selecting Tab cycles through the list. Releasing selects the highlighted application window.
The Application key has an image of a mouse pointer on a menu (between the Alt and Ctrl keys ( ) to the right of your Space Bar). Depressing this key will display the selected item’s shortcut window. This is the menu that is displayed by right-clicking.
Insert a space between words. It is suggested that you utilize Tabs (or other formatting commands) to put distance between elements. Using the space bar to insert visual space works but would not be considered a best practice in page design. Double spaces between sentences are no longer required. This is a carryover from the days of fixed width fonts on a typewriter such as Courier, Orator, Prestige Elite, etc.
Pressing the Space Bar while viewing a web page in Internet Explorer will scroll the page downwards. Shift + Space Bar will scroll the page upwards.
Creates a new Paragraph <p> ( ) or what is referred to as a Hard Return. In any dialog box a selected button or command can be selected by depressing this key. Selected buttons can be recognized by their darker (dotted) borders, or what is referred to as Focus.
Creates a new Line Break <br> ( ) or what is referred to as a Soft Return.
Shift + Arrow Up, Down, Left or Right. Position your cursor at the beginning of the area you wish to highlight for copying. Now use the up, down, left or right arrow keys to select areas of content to be highlighted, copied, pasted, etc.
While working with text, use this key to delete characters to the left of the insertion point.
Depress and hold the Ctrl key as you select Home to go to the first line of a document.
In a browser window use the Page Up key to move up one full screen on a web page.
While working with text, use this key to delete characters to the right of the insertion point. This key can also be used to delete selected files. If you use the keyboard combination Shift + Delete the item is permanently deleted, bypassing the Recycle Bin.
Depress and hold the Ctrl key as you select End to go to the last line of a document.
In a browser window use the Page Down key to move down one full screen on a web page.
Navigate in a document to the line above. Hold the Ctrl key down as you press this key to move to the beginning of the second line above.
Navigate in a document one character to the right. Hold the Ctrl key down as you press this key to move one word to the right.
Navigate in a document to the line below. Hold the Ctrl key down as you press this key to move to the beginning of the second line below.
Navigate in a document one character to the left. Hold the Ctrl key down as you press this key to move one word to the left.
If you want to use the numeric keypad on the right end of the keyboard to display numbers, the Num Lock key must be selected (usually a light above the Num Lock will indicate that it is on). If you want to use the keypad to navigate within a document, turn off Num Lock by pressing the key (the light will go off).
In Windows Explorer this expands everything under the current selection. Caution: do not try this with the C Drive icon selected.
– (Minus Sign)
In Windows Explorer this collapses the current selection.
+ (Plus Sign)
In Windows Explorer this expands the current selection.
Here is a link to a picture of a clickable Windows Keyboard with detailed explanations of each key. Use your back button to return to this page.
The desktop (overview)
The desktop is the main screen area that you see after you turn on your computer and log on to Windows. Like the top of an actual desk, it serves as a surface for your work. When you open programs or folders, they appear on the desktop. You can also put things on the desktop, such as files and folders, and arrange them however you want.
The desktop is sometimes defined more broadly to include the taskbar. The taskbar sits at the bottom of your screen. It shows you which programs are running and allows you to switch between them. It also contains the Start button , which you can use to access programs, folders, and computer settings.
Working with desktop icons
Icons are small pictures that represent files, folders, programs, and other items. When you first start Windows, you’ll see at least one icon on your desktop: The Recycle Bin (more on that later). Your computer manufacturer might have added other icons to the desktop. Some examples of desktop icons are shown below.
Examples of desktop icons
Double-clicking a desktop icon starts or opens the item it represents.
Adding and removing icons from the desktop
You can choose which icons appear on the desktop—you can add or remove an icon at any time. Some people like a clean, uncluttered desktop with few or no icons. Others place dozens of icons on their desktop to give them quick access to frequently used programs, files, and folders.
If you want easy access from the desktop to your favorite files or programs, you can create shortcuts to them. A shortcut is an icon that represents a link to an item, rather than the item itself. When you double-click a shortcut, the item opens. If you delete a shortcut, only the shortcut is removed, not the original item. You can identify shortcuts by the arrow on their icon.
A file icon (left) and a shortcut icon (right)
To add a shortcut to the desktop
Right-click the item, click Send to, and then click Desktop (create shortcut). The shortcut icon appears on your desktop.
To add or remove common desktop icons
Common desktop icons include Computer, your personal folder, the Recycle Bin, and Control Panel.
Right-click an empty area of the desktop, and then click Personalize.
In the left pane, click Change desktop icons.
Under Desktop icons, select the check box for each icon that you want to add to the desktop, or clear the check box for each icon that you want to remove from the desktop, and then click OK.
To move a file from a folder to the desktop
Open the folder that contains the file.
Drag the file to the desktop.
To remove an icon from the desktop
Right-click the icon, and then click Delete. If the icon is a shortcut, only the shortcut is removed; the original item is not deleted.
Moving icons around
Windows stacks icons in columns on the left side of the desktop. But you’re not stuck with that arrangement. You can move an icon by dragging it to a new place on the desktop.
You can also have Windows automatically arrange your icons. Right-click an empty area of the desktop, click View, and then click Auto arrange icons. Windows stacks your icons in the upper-left corner and locks them in place. To unlock the icons so that you can move them again, click Auto arrange icons again, clearing the check mark next to it.
By default, Windows spaces icons evenly on an invisible grid. To place icons closer together or with more precision, turn off the grid. Right-click an empty area of the desktop, point to View, and then click Align icons to grid to clear the check mark. Repeat these steps to turn the grid back on.
Selecting multiple icons
To move or delete a bunch of icons at once, you must first select all of them. Click an empty area of the desktop and drag the mouse. Surround the icons that you want to select with the rectangle that appears. Then release the mouse button. Now you can drag the icons as a group or delete them.
Select multiple desktop icons by dragging a rectangle around them
Hiding desktop icons
If you want to temporarily hide all of your desktop icons without actually removing them, right-click an empty part of the desktop, click View, and then click Show desktop items to clear the check mark from that option. Now no icons are displayed on the desktop. You can get them back by clicking Show desktop items again.
The Recycle Bin
When you delete a file or folder, it doesn’t actually get deleted right away—it goes to the Recycle Bin. That’s a good thing, because if you ever change your mind and decide you need a deleted file, you can get it back. For more information, see Recover files from the Recycle Bin.
The Recycle Bin when empty (left) and full (right)
If you’re sure that you won’t need the deleted items again, you can empty the Recycle Bin. Doing that will permanently delete the items and reclaim any disk space they were using. For more information, see Permanently delete files from the Recycle Bin.
Temporarily preview the desktop using Aero Peek
You can temporarily view the desktop using Aero Peek. This can be useful for quickly viewing desktop gadgets and folders, or when you don’t want to minimize all open windows and then have to restore them.
Quickly view your desktop gadgets using Peek
To temporarily preview the desktop
Point your mouse to the Show desktop button at the end of the taskbar. The open windows fade from view, revealing the desktop.
To make the windows reappear, move the mouse away from the Show desktop button.
Press Windows logo key +Spacebar to temporarily preview the desktop. To restore the desktop, release Windows logo key +Spacebar.
To minimize open windows so that they remain minimized, click the Show desktop button, or press Windows logo key +D. To restore the open windows, click the Show desktop button again or press Windows logo key +D again.
To turn off desktop previews
If you don’t want the desktop to fade when you point your mouse to the Show desktop button, you can turn off this feature of Peek.
Under Preview desktop with Aero Peek, clear the Use Aero Peek to preview the desktop check box.
You can also use Peek to preview an open window on the desktop (and temporarily make other open windows fade). For more information about this feature of Peek, see Preview an open window on the desktop using Aero Peek.
The taskbar (overview)
In this article
The Start button , which opens the Start menu. See The Start menu (overview).
The middle section, which shows you which programs and files you have open and allows you to quickly switch between them.
You’re likely to use the middle section of the taskbar the most, so let’s look at it first.
Keep track of your windows
If you open more than one program or file at a time, you can quickly start piling up open windows on your desktop. Because windows often cover each other or take up the whole screen, it’s sometimes hard to see what else is underneath or remember what you’ve already opened.
That’s where the taskbar comes in handy. Whenever you open a program, folder, or file, Windows creates a corresponding button on the taskbar. The button shows an icon that represents the open program. In the picture below, two programs are open—Calculator and Minesweeper—and each has its own button on the taskbar.
Each program has its own button on the taskbar
Notice how the taskbar button for Minesweeper is highlighted. That indicates that Minesweeper is the active window, meaning that it’s in front of any other open windows and is ready for you to interact with.
To switch to another window, click its taskbar button. In this example, clicking the taskbar button for Calculator brings its window to the front.
Click a taskbar button to switch to that window
Clicking taskbar buttons is one of several ways to switch between windows. For more information, see Working with windows.
Minimize and restore windows
When a window is active (its taskbar button is highlighted), clicking its taskbar button minimizes the window. That means that the window disappears from the desktop. Minimizing a window doesn’t close it or delete its contents—it temporarily removes it from the desktop.
In the picture below, Calculator is minimized, but not closed. You can tell it’s still running because it has a button on the taskbar.
Minimizing Calculator leaves only its taskbar button visible
You can also minimize a window by clicking the minimize button in the upper-right corner of the window.
Minimize button (left)
To restore a minimized window (make it show up again on the desktop), click its taskbar button. For more information about these buttons, see Working with windows.
See previews of your open windows
When you move your mouse pointer to a taskbar button, a small picture appears that shows you a miniature version of the corresponding window. This preview, also called a thumbnail, is especially useful. And if one of your windows has video or animation playing, you’ll see it playing in the preview.
You can see thumbnails only if Aero can run on your computer and you’re running a Windows 7 theme.
The notification area
The notification area, on the far right side of the taskbar, includes a clock and a group of icons. It looks like this.
The notification area of the taskbar
These icons communicate the status of something on your computer or provide access to certain settings. The set of icons you see depends on which programs or services you have installed and how your computer manufacturer set up your computer.
When you move your pointer to a particular icon, you will see that icon’s name or the status of a setting. For example, pointing to the volume icon shows the current volume level of your computer. Pointing to the network icon displays information about whether you are connected to a network, the connection speed, and the signal strength.
Double-clicking an icon in the notification area usually opens the program or setting associated with it. For example, double-clicking the volume icon opens the volume controls. Double-clicking the network icon opens Network and Sharing Center.
Occasionally, an icon in the notification area will display a small pop-up window (called a notification) to notify you about something. For example, after adding a new hardware device to your computer, you might see this.
Click the Close button in the upper-right corner of the notification to dismiss it. If you don’t do anything, the notification will fade away on its own after a few seconds.
To reduce clutter, Windows hides icons in the notification area when you haven’t used them in a while. If icons become hidden, click the Show hidden icons button to temporarily display the hidden icons.
Customize the taskbar
There are many ways to customize the taskbar to suit your preferences. For example, you can move the entire taskbar to the left, right, or top edge of the screen. You can make the taskbar larger, have Windows automatically hide it when you’re not using it, and add toolbars to it.
What’s new with the Windows 7 taskbar?
In Windows 7, the taskbar has been completely redesigned to help you more easily manage and access your most important files and programs.
Taskbar icons have a new look and do more than just show you which programs are running.
In the default view, each program appears as a single, unlabeled icon—even when multiple items for a program are open—for a clean and uncluttered look. You can customize the taskbar appearance to change how icons appear and how they group together when you have multiple items open. You can also choose to see individual buttons for each open file. For more information, see Change how icons appear on the taskbar.
You can also rearrange and organize program icons on the taskbar, including pinned programs and running programs that aren’t pinned, so they appear in the order you prefer. To rearrange the order of program icons on the taskbar, drag an icon from its current position to a different position on the taskbar. You can rearrange program icons as often as you like.
Previewing open windows with Aero Peek
When you open multiple windows on the desktop, sometimes it can be a challenge to view separate windows and switch between them.
You can use Aero Peek to take a quick look at other open windows without clicking away from the window you are currently working on. Point your mouse to a taskbar icon, and thumbnail previews of any open windows associated with that icon appear above the taskbar. If you want to open a window you are previewing, just click its thumbnail. For more information, see Preview an open file on the desktop using Aero Peek.
Pinning programs to the taskbar complements pinning programs to the Start menu, like in earlier versions of Windows. When you pin a favorite program to the taskbar, you can always see it there and easily access it with a single click. Windows 7 also includes Jump Lists, so that in addition to launching a program from the taskbar, you can now launch favorite and recent items from that program, just by clicking the same icon.
Jump Lists are lists of recently or frequently opened items, such as files, folders, tasks, or websites, organized by the program that you use to open them. In addition to being able to open recent items using a Jump List, you can also pin favorite items to a Jump List so you can quickly get to the items that you use every day.
On the taskbar, Jump Lists appear for programs that you’ve pinned to the taskbar and programs that are currently running. You can view the Jump List for a program by right-clicking the taskbar icon, or by dragging the icon toward the desktop. You open items from the Jump List by clicking them.
A new way of managing the notification area on the end of the taskbar means you get fewer notifications, and the ones you get are collected in a single place in Windows.
In the past, the notification area could sometimes become cluttered with icons. Now, you can choose which icons appear visible at all times. And you can keep the rest of the icons on hand in an overflow area, where they’re accessible with a single mouse click. For more information about customizing the notification area, see Change how icons appear in the notification area of the taskbar.
Action Center is a single area that collects important notification messages about security and maintenance settings. You can review these messages later if you don’t want to be interrupted. When you click the Action Center icon and then click Open Action Center, you’ll see information about the things you need to take action on, and find helpful links to troubleshooters and other tools that can help fix problems. For more information, see What is Action Center?
Viewing the desktop
The Show desktop button has been moved the opposite end of the taskbar from the Start button, making it easier to click or point at the button without accidentally opening the Start menu.
Show desktop button on the taskbar
In addition to clicking the Show desktop button to get to the desktop, you can temporarily view or peek at the desktop by just pointing your mouse at the Show desktop button, without clicking it. When you point at the Show desktop button at the end of the taskbar, any open windows fade from view, revealing the desktop. To make the windows reappear, move the mouse away from the Show desktop button.
This can be useful for quickly viewing desktop gadgets, or when you don’t want to minimize all open windows and then have to restore them. For more information, see Temporarily preview the desktop using Aero Peek.
The Start menu (overview)
In this article
The Start menu is the main gateway to your computer’s programs, folders, and settings. It’s called a menu because it provides a list of choices, just as a restaurant menu does. And as “start” implies, it’s often the place that you’ll go to start or open things.
Use the Start menu to do these common activities:
Open commonly used folders
Search for files, folders, and programs
Adjust computer settings
Get help with the Windows operating system
Turn off the computer
Log off from Windows or switch to a different user account
Getting started with the Start menu
To open the Start menu, click the Start button in the lower-left corner of your screen. Or, press the Windows logo key on your keyboard.
The Start menu is divided into three basic parts:
The large left pane shows a short list of programs on your computer. Your computer manufacturer can customize this list, so its exact appearance will vary. Clicking All Programs displays a complete list of programs (more on this later).
At the bottom of the left pane is the search box, which allows you to look for programs and files on your computer by typing in search terms.
The right pane provides access to commonly used folders, files, settings, and features. It’s also where you go to log off from Windows or turn off your computer.
Opening programs from the Start menu
One of the most common uses of the Start menu is opening programs installed on your computer. To open a program shown in the left pane of the Start menu, click it. The program opens and the Start menu closes.
If you don’t see the program you want, click All Programs at the bottom of the left pane. Instantly, the left pane displays a long list of programs in alphabetical order, followed by a list of folders.
Clicking one of the program icons launches the program, and the Start menu closes. So what’s inside the folders? More programs. Click Accessories, for example, and a list of programs that are stored in that folder appears. Click any program to open it. To get back to the programs you saw when you first opened the Start menu, click Back near the bottom of the menu.
If you’re ever unsure what a program does, move the pointer over its icon or name. A box appears that often contains a description of the program. For example, pointing to Calculator displays this message: “Performs basic arithmetic tasks with an on-screen calculator.” This trick works for items in the right pane of the Start menu, too.
You might notice that over time, the lists of programs in your Start menu change. This happens for two reasons. First, when you install new programs, they get added to the All Programs list. Second, the Start menu detects which programs you use the most, and places them in the left pane for quick access.
The search box
The search box is one of the most convenient ways to find things on your computer. The exact location of the items doesn’t matter—the search box will scour your programs and all of the folders in your personal folder (which includes Documents, Pictures, Music, Desktop, and other common locations). It will also search your e‑mail messages, saved instant messages, appointments, and contacts.
The Start menu search box
To use the search box, open the Start menu and start typing. You don’t need to click inside the box first. As you type, the search results appear above the search box in the left pane of the Start menu.
A program, file, or folder will appear as a search result if:
Any word in its title matches or begins with your search term.
Any text in the actual contents of the file—such as the text in a word-processing document—matches or begins with your search term.
Any word in a property of the file, such as the author, matches or begins with your search term. (For more information about file properties, see Add tags and other properties to a file.)
Click any search result to open it. Or, click the Clear button to clear the search results and return to the main programs list. You can also click See more results to search your entire computer.
Besides programs, files and folders, and communications, the search box also looks through your Internet favorites and the history of websites you’ve visited. If any of these webpages include the search term, they appear under a heading called “Favorites and History.”
What’s in the right pane?
The right pane of the Start menu contains links to parts of Windows that you’re likely to use frequently. Here they are, from top to bottom:
Personal folder. Opens your personal folder, which is named for whoever is currently logged on to Windows. For example, if the current user is Molly Clark, the folder will be named Molly Clark. This folder, in turn, contains user-specific files, including the Documents, Music, Pictures, and Videos folders.
Documents. Opens the Documents folder, where you can store and open text files, spreadsheets, presentations, and other kinds of documents.
Pictures. Opens the Pictures folder, where you can store and view digital pictures and graphics files.
Music. Opens the Music folder, where you can store and play music and other audio files.
Games. Opens the Games folder, where you can access all of the games on your computer.
Computer. Opens a window where you can access disk drives, cameras, printers, scanners, and other hardware connected to your computer.
Control Panel. Opens Control Panel, where you can customize the appearance and functionality of your computer, install or uninstall programs, set up network connections, and manage user accounts.
Devices and Printers. Opens a window where you can view information about the printer, mouse, and other devices installed on your computer.
Default Programs. Opens a window where you can choose which program you want Windows to use for activities such as web browsing.
Help and Support. Opens Windows Help and Support, where you can browse and search Help topics about using Windows and your computer. See Getting help.
At the bottom of the right pane is the Shut down button. Click the Shut down button to turn off your computer.
Clicking the arrow next to the Shut down button displays a menu with additional options for switching users, logging off, restarting, or shutting down. For more information, see Log off from Windows and Turn off a computer: frequently asked questions.
Click the Shut down button to shut down your computer or click the arrow for more options
Customize the Start menu
You can control which items appear in the Start menu. For example, you can pin icons for your favorite programs to the Start menu for easy access, or remove programs from the list. You can also choose to hide or display certain items in the right pane. See Customize the Start menu for more information.
Example of a shortcut on the desktop
Add or delete desktop icons
Most of the icons you add to your desktop will be shortcuts, but you can also save files or folders to the desktop. If you delete files or folders that are stored on your desktop, they are moved to the Recycle Bin, where you can permanently delete them. If you delete a shortcut, the shortcut is removed from your desktop, but the file, program, or location that the shortcut links to is not deleted.
You can identify shortcuts by the arrow on their icon.
To add an icon
Locate the item that you want to create a shortcut for.
Right-click the item, click Send to, and then click Desktop (create shortcut). The shortcut icon appears on your desktop.
For help with finding a file or folder, see Find a file or folder.
To delete an icon
Right-click an icon on the desktop, click Delete, and then click Yes. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
To add or remove common desktop icons
You can add or remove special Windows desktop icons, including shortcuts to the Computer folder, your personal folder, the Network folder, the Recycle Bin, and Control Panel. If you remove one of these special icons from view, you can always add it back.
In the left pane, click Change desktop icons.
Under Desktop Icons, select the check box for each icon that you want to add to the desktop, or clear the check box for each icon that you want to remove from the desktop, and then click OK.
Taskbar: recommended links
Show or hide the Recycle Bin
The Recycle Bin usually appears on the desktop. If you don’t see the Recycle Bin, don’t panic—it might just be hidden.
To show or hide the Recycle Bin on the desktop
Click the Start button , type desktop icons into the search box, and then click Show or hide common icons on the desktop.
In the Desktop Icon Settings dialog box, do one of the following:
To hide the Recycle Bin, clear the Recycle Bin check box.
To show the Recycle Bin, select the Recycle Bin check box.
Even when the Recycle Bin is hidden, deleted files are still stored there temporarily until you choose to permanently delete them or recover them. For more information, see Permanently delete files from the Recycle Bin or Recover files from the Recycle Bin.
Show, hide, or resize desktop icons
To show desktop icons
Right-click the desktop, point to View, and then click Show desktop icons.
To hide desktop icons
Right-click the desktop, point to View, and then click Show desktop icons to clear the check mark.
Hiding all of the icons on your desktop doesn’t delete them, it just hides them until you choose to show them again.
To resize desktop icons
Right-click the desktop, point to View, and then click Large icons, Medium icons, or Small icons.
You can also use the scroll wheel on your mouse to resize desktop icons. On the desktop, press and hold Ctrl while you scroll the wheel to make icons larger or smaller.
For information on how to show or hide individual Windows icons, such as the icon for Computer or Recycle Bin, see Show or hide common icons on the desktop.
Change your desktop background (wallpaper)
Your desktop background (also called wallpaper) can be a digital picture from your personal collection, a picture that comes with Windows, a solid color, or a picture framed with a color. You can choose one image to be your desktop background or you can display a slide show of pictures. For more information, see Create a desktop background slide show and Make changes to your desktop background slide show.
Windows comes with lots of desktop background choices
To change the desktop background
Click the picture or color that you want to use for your desktop background.
If the picture you want to use isn’t in the list of desktop background pictures, click an item in the Picture location list to see other categories, or click Browse to search for the picture on your computer. When you find the picture that you want, double-click it. It will become your desktop background.
Look for pictures in other locations on your computer
Under Picture position, click the arrow and choose whether to crop the picture to fill the screen, fit the picture to the screen, stretch the picture to fit the screen, tile the picture, or center the picture on the screen, and then click Save changes.
If you choose to have a fitted or centered picture as your desktop background, you can also frame your picture with a color background. Under Picture position, click Fit or Center. Click Change background color, click a color, and then click OK.
To make any picture stored on your computer (or a picture you are currently viewing) your desktop background, right-click the picture, and then click Set as Desktop Background.
The Set as Desktop Background option
Show, hide, or resize desktop icons
To show desktop icons
Right-click the desktop, point to View, and then click Show desktop icons.
To hide desktop icons
Right-click the desktop, point to View, and then click Show desktop icons to clear the check mark.
Hiding all of the icons on your desktop doesn’t delete them, it just hides them until you choose to show them again.
To resize desktop icons
Right-click the desktop, point to View, and then click Large icons, Medium icons, or Small icons.
You can also use the scroll wheel on your mouse to resize desktop icons. On the desktop, press and hold Ctrl while you scroll the wheel to make icons larger or smaller.
For information on how to show or hide individual Windows icons, such as the icon for Computer or Recycle Bin, see Show or hide common icons on the desktop.
Show or hide common icons on the desktop
In the left pane, click Change desktop icons.
Under Desktop Icons, select the check box for each icon that you want to appear on the desktop. Clear the check box for icons that you don’t want to appear, and then click OK.
Minimize all open windows to view the desktop
There are different ways to minimize all of your open windows at once.
Show desktop button on the taskbar
To minimize open windows using the mouse
To minimize open windows using the keyboard
Press the Windows logo key +D. (To restore minimized windows, press the Windows logo key +D again.)
You can also press the Windows logo key +M to minimize open windows, and press the Windows logo key +Shift+M to restore them.
What’s new with the Windows desktop?
In this article
New features on the Windows desktop make it easier to organize and manage multiple windows. You can switch easily between open windows so that you can focus on important programs and files. Other new features help you add a personal touch to your desktop.
You can use Snap to arrange and resize windows on the desktop with a simple mouse movement. Using Snap, you can quickly align windows at the side of the desktop, expand them vertically to the entire height of the screen, or maximize them to completely fill the desktop. Snap can be especially helpful when comparing two documents, copying or moving files between two windows, maximizing the window you’re currently working on, or expanding long documents so they’re easier to read and require less scrolling.
Drag a window to the side of the desktop to expand it to half of the screen
To use Snap, drag the title bar of an open window to either side of the desktop to align it there, or drag it to the top of the desktop to maximize the window. To expand a window vertically using Snap, drag the top edge of the window to the top of the desktop. For more information, search for “Snap” in Help and Support.
Using Shake, you can quickly minimize all open windows on the desktop except the one you want to focus on. Just click the title bar of the window you want to keep open and drag (or shake) the window back and forth quickly, and the other open windows are minimized.
Shake a window to minimize all other windows
To restore the minimized windows, shake the open window again. For more information, see Minimize windows on the desktop using Shake.
You can use Aero Peek features to quickly preview the desktop without minimizing all your windows, or preview an open window by pointing at its icon on the taskbar.
The Show desktop button has been moved the opposite end of the taskbar from the Start button, making it easier to click or point at the button without accidentally opening the Start menu.
In addition to clicking the Show desktop button to get to the desktop, you can temporarily view or peek at the desktop by just pointing your mouse at the Show desktop button. When you point at the Show desktop button at the end of the taskbar, any open windows fade from view, revealing the desktop. To make the windows reappear, move the mouse away from the Show desktop button.
Quickly view your desktop using Peek
This can be useful for quickly viewing desktop gadgets, or when you don’t want to minimize all open windows and then have to restore them. For more information, see Temporarily preview the desktop using Aero Peek.
You can also use Aero Peek to take a quick look at other open windows without clicking away from the window you are currently working on.
Peek at open windows using thumbnails on the taskbar
Point your mouse at a program icon on the taskbar that has open files. Thumbnail previews of any open files associated with that program appear above the taskbar. You can point at a thumbnail to preview that window’s contents, and all the other open windows on the desktop fade away to reveal just the window you’re previewing. To open the window you’re previewing, click the thumbnail. For more information, see Preview an open file on the desktop using Aero Peek.
Windows Sidebar isn’t included in this version of Windows. Instead, you can display gadgets anywhere on your desktop and use the Aero Peek features to temporarily view your desktop gadgets without minimizing or closing the windows you’re working with.
Gadgets on the desktop
For more information about using gadgets on your desktop, search for “gadgets” in Help and Support.
Your desktop background doesn’t have to be a single picture anymore. With Windows 7, you can display a slide show of pictures, instead. Some Windows themes include a slide show, or you can create your own slide show from your personal collection of pictures. For more information about setting up a slide show background, see Create a desktop background slide show.
Not all new desktop features are available in all editions of Windows 7. For example, Aero Peek, Shake, and background slide shows are not included in Windows 7 Home Basic or Windows 7 Starter. You can find out which edition of Windows 7 you have on your computer by opening System in Control Panel.
Create a desktop background slide show
You can have a slide show (a rotating series of pictures) as your desktop background. You can use your own pictures or pictures that Windows provides as part of a theme.
To use your own pictures
Find the pictures that you want to include in your slide show. All of the pictures must be located in the same folder.
If the pictures that you want to use aren’t in the list of desktop background pictures, click the Picture location list to view other categories, or click Browse to search your computer for the folder where the pictures are located.
Look for pictures in other locations on your computer
Select the check box for each picture that you want to include in your slide show.
By default, all of the pictures in a folder are selected and will be part of the slide show. If you don’t want all of the pictures in the folder to be included, do one of the following:
Clear the check box for each picture that you want to remove from the slide show.
Clear the check box to remove a picture from the slide show.
Press the Ctrl key, and then click each picture that you want to remove. Only the selected pictures will appear in the slide show.
To create a slide show of pictures on the desktop, you must select more than one picture. If only one picture is selected, the slide show ends and the selected picture becomes the desktop background.
If all of the pictures in the folder are selected, any new pictures that you add to the folder will be added to the slide show automatically.
Do one or more of the following:
Click an item in the Picture position list to crop the pictures to fill the screen, fit the pictures to the screen, stretch the pictures to fit the screen, tile the pictures, or center the pictures on the screen.
Click an item in the Change picture every list to choose how quickly the slide show changes pictures.
Select the Shuffle check box to have the pictures appear in a random order.
Click Save changes.
To use pictures that Windows provides as part of a theme
Under Aero Themes, click a theme to apply it to the desktop. With the exception of the Windows 7 theme, all of the Aero themes include a desktop background slide show.
To change the theme’s default slide show pictures or settings, click Desktop Background.
Select the check box for each picture that you want to include in your slide show.
By default, all of the pictures associated with a theme are selected and will be part of the slide show. To add pictures from other themes to your slide show, do one of the following:
Point to each picture that you want to add to the slide show, and then select its check box.
Point to a picture, and then select its check box to add it to the slide show.
Press and hold the CTRL key, and then click each of the pictures that you want to add. Only the selected pictures will appear in the slide show.
To create a slide show of pictures on the desktop, you must select more than one picture. If only one picture is selected, the slide show ends and the selected picture becomes the desktop background.
To change the slide show’s settings, do one or more of the following:
Click an item in the Picture position list to crop the pictures to fill the screen, fit the pictures to the screen, stretch the pictures to fit the screen, tile the pictures, or center the pictures on the screen.
Click an item in the Change picture every list to choose how quickly the slide show changes pictures.
Select the Shuffle check box to have the pictures appear in a random order.
Click Save changes.
Your slide show will be part of the unsaved theme that appears under My Themes.
For information about customizing and saving themes, see Customize a theme
For information about customizing a desktop background slide show, see Make changes to your desktop background slide show.
six Windows 7 editions. Two editions for mainstream
consumers and business users and four specialized editions for enterprise
customers, technical enthusiasts, emerging markets, and entry level PCs. The
design of each edition matches the demands of particular user types. You may
need more than one edition in your environment; therefore, it is important to
understand each edition’s features.
Each edition requires activation to verify that your copy of Windows is genuine and that it has not been used on more computers than the Microsoft Software License Terms allow. In this way, activation helps prevent software counterfeiting. With an activated copy of Windows, you can use every Windows feature for that specific edition.
You have 30 days after installing Windows to activate it online or by telephone. If this 30-day period expires before you complete activation, Windows will stop working. If this happens, you cannot create new files or save changes to existing ones. You can regain full use of your computer by activating your Windows copy.
|Windows 7 edition|
Windows 7 Starter edition
Windows 7 Starter is targeted specifically for small form factor PCs in all markets. It is only available for the 32-bit platform. This edition features:
1. Improved Windows Taskbar and Jump Lists
2. Windows Search
3. Ability to join a HomeGroup
4. Action Center, Device StageTM, and Windows® Fax and Scan
5. Enhanced media streaming, including Play To
6. Broad applications and device compatibility
7.Ability to run as many applications simultaneously
8.Secured, reliable, and supported operating system
Windows 7 Home Basic edition
Windows 7 Home Basic is targeted for value PCs in emerging markets, meant for accessing the internet and running basic productivity applications. This edition includes all of the features available in Windows 7 Starter. Additionally, it includes :
1.No limit on the number of programs you can run
2.Live Thumbnail previews and enhanced visual experiences
3.Advanced networking support (ad hoc wireless networks and internet connection sharing)
Windows 7 Home Premium edition
Windows 7 Home Premium is the standard edition for customers. It provides full functionality on the latest hardware, simple ways to connect, and a visually rich environment. This edition includes all features available in Windows 7 Home Basic in addition to the following:
1. Windows® Aero®, advanced Windows navigation and Aero background
2. Windows® Touch (Multi-touch and handwriting support)
3. Ability to create a HomeGroup, which eases sharing across all PCs and devices
4. DVD Video playback and authoring
5. Windows® Media Center, Snipping Tool, Sticky Notes, Windows Journal, and Windows® SideshowTM
Windows 7 Professional edition
Windows 7 Professional is the business-focused edition for small and lower mid-market companies and users who have networking, backup, and security needs and multiple PCs or servers. It includes all features available in Windows 7 Home Premium in addition to the following:
1. Core business features, such as Domain Join and Group Policy
2. Data protection with advanced network backup and Encrypted File System
3. Ability to print to the correct printer at home or work with Location Aware Printing
4. Remote Desktop host and Offline folders
5. Windows Virtual PC and Windows XP Mode
Windows 7 Enterprise edition
Windows 7 Enterprise provides advanced data protection and information access for businesses that use IT as a strategy asset. It is a business-focused edition, targeted for managed environments, mainly large enterprises. This edition includes all features available in Windows 7 Professional in addition to the following:
1. BitLocker and BitLocker To Go data protection for internal and external drives
2. AppLocker to prevent unauthorized software installation and execution
3. DirectAccess, which provides seamless connectivity to a corporate network
4. BranchCache, which decreases the amount of time for branch office workers to access files across the corporate network
5. All worldwide interface languages
6. Enterprise Search Scopes
7. Virtual Desktop Infrastructure (VDI) enhancements and the ability to start from a VHD
Windows 7 Ultimate edition
Windows 7 Ultimate is targeted for technical enthusiasts who want all Windows 7features without a Volume License agreement. It includes all of the same features as the Windows 7 Enterprise. Windows 7 Ultimate is not licensed for VDI scenarios.
Windows 7 System Requirements Finalized
System requirements for Windows 7 aren’t any great mystery, but now we’re getting a much better idea of what it’ll say on the retail box.
Microsoft posted relatively modest system requirements (at least for any computer belonging to a Tom’s Hardware reader) when it released the Windows 7 public beta in January and only slightly modified them for the release of yesterday’s Release Candidate.
The system requirements for the beta at the time called for:
1 GHz 32-bit or 64-bit processor
1 GB of system memory
16 GB of available disk space
Support for DirectX 9 graphics with 128 MB memory (to enable the Aero theme)
The system requirements published yesterday for the official Release Candidate are the following:
1 GHz or faster 32-bit (x86) or 64-bit (x64) processor
1 GB of RAM (32-bit)/2 GB of RAM (64-bit)
16 GB of available disk space (32-bit)/20 GB (64-bit)
DirectX 9 graphics device with Windows Display Driver Model 1.0 or higher driver
The only real changes to the system requirements since January are slightly bumped up ones for the 64-bit version, though we suspect anyone who plans to run the x64 build will have a machine that’s way beyond the minimum (having at least 4 GB of RAM would be a good starting point).
While the system requirements posted yesterday apply to the Release Candidate, Microsoft told ZDNet that they were ‘final’, though it’s unknown if there will be different requirements between different SKUs such as Starter Edition or Ultimate Edition. “The system requirements are final and not SKU-specific,” said a Microsoft spokesperson.
Those who plan to run XP Mode will need at least 2 GB RAM, 15 GB of additional hard drive space and a processor that supports hardware virtualization.
According to early tests, Windows 7 performs better than Windows Vista on the same hardware.
“It’s been a long time since we’ve had a version of Windows that will actually run better [than the previous version] on the hardware that most customers have,” Mike Nash, corporate vice president of Microsoft’s Windows product management group, said during a conference call with reporters, quoted byComputerWorld.
Windows 7 does carry with it slightly heftier system requirements than Vista does, despite it being a better performer. From one generation to the next – and three years later – Windows 7’s system demands does seem positively modest.
For reference, Windows Vista’s system requirements are:
1 GHz processor (32- or 64-bit)
512 MB of RAM (for Home Basic); 1 GB of RAM for all other versions
15 GB of available disk space
Support for DirectX 9 graphics and 32 MB of graphics memory (for Home Basic); 128 MB of graphics memory plus WDDM support for all other versions