typoweheeElectronics - Devices

Nov 8, 2013 (4 years and 8 months ago)







Compiled by:

N. S. Naga Prasad:


B.B.S. Devnar School for the Blind:

Mayur Narg Line:









This is the age of computers. The word "Computer" itself means that which









History Of Com



Generation of Computers:



Characteristics of Computers:



Classification Of Computers:






Components of a computer:









Parts of Computer:





Computer is an electronic device.
Computer is a data processing tool. It takes Data and
commands as input. Computer processes the data according to the commands and provides the
resulting information as an output.


A computer is a machine, which calculates and solves problems at very fast speed and
has memory to store instructions and information’s. It can also do so many other interesting
works like drawing different shapes and pictures. We can
also listen music on it. We can play
games, solve problems like quiz, puzzles etc and can also make cards like greeting cards, birth day
cards etc. Computer can compare and also calculates the figures. It has the storage place called
memory to store the

information’s. This memory is in the form of small boxes called chips. The
word compute means to calculate and err means to work on. So compute and er are the two words
which makes computer.

This is the age of computers. The word "Computer" itself m
eans that which







This device (machine) that processes information is called computer.




Since the computer has become an essential part of our life, let us see
its applications in various

In Education:


Computers can play a major role in educating students. Since the advent of the
multi media computers, various CDs having educational titles have been produced especially for
students. There are a lot of soft ware, such as multi
media encyclopedias, multimedia dictionaries
… these are available to impact you basic and advanced knowledge on various subjects. Now, you
even have the prescribed books that you study in your schools, available on CD ROMs, which have
sound, graphics and

even animation to make topics that you need to study, very interesting and
captivating. Software is written in such a way that they encourage learning by the use of
interactive models of actual processes.

Like concept of ‘Lever’ can easily be explained b
y showing
animation of the wooden board being used as a lever. This would have been difficult to explain
through a mere classroom lecture. This type of learning is called Computer Aided Learning

In Business:


Now with the increased awareness of co
mputers, all large or small sized businesses
have increased their efficiency and minimized the cost of operation by using computers in various
types of applications.


roll and Personnel Management:


Salaries are calculated in a computerized process af
involving lots of factors like number of hours worked, leaves taken etc., and many more factors
which involve lot of human effort. Also personnel records are maintained on computer files which
include details of the persons working like name, age, date

of joining, salary etc.

Sales and Stock Control:



must have seen lots of business stores printing bills on computers.
Computer automatically calculates the bills after the item code of item purchased is entered
because all item codes and correspondi
ng item names,

their prices and quantity in store is already
fed into the computer. Also every item sold will deduct one item from the items in stock. So when
an item is going to be out of the stock, a warning message will flash, telling the store person t
o re
order the stock for that particular item.

At Hospitals:



are of great help in the medical profession. Robotic arms are now
available for surgical procedures, which can be used with great precision on the instructions of a
surgeon. Computer
s are also used to calculate and administer accurate doses of radiotherapy to
cancer patients. Most of the advanced tests use computers as an aid. For example, the
ElectroCardioGram (ECG) is used for the detection of heart diseases, the ElectroEncephaloGra
(EEG) is used for the study of the brain functioning to detect for neurological disorders, in
Magnetic Resonance Imaging (MRI) an organ is imaged to produce an X
ray image at a very high

These are simply a few techniques which use ‘computers’

in medicine. In an operation theatre and
in intensive care units, virtually every major organ system in the body is monitored for its
functioning with the help of computers. Just imagine the importance of ‘computers’ in surgery.

In Science and Engineerin


has a major part to play in the advancement of
technology. From the field of entertainment and computer graphics to the launching of satellites
and guiding of missiles on their targets, computer is being used extensively. Computers have also
greatly accelerated and expanded research in various branches of science like Physics, Chemistry,
Astronomy and Genetics.

These days computerized sewing machines, which can do a lot of embroidery
work very beautifully and efficiently, are available in the
market. You can also get some
sophisticated cameras which have a small computer inside, which manages the amount of
aperture and shutter speed itself according to the available light. You can also see cars
with computer controlled fuel mixing. The applica
tion of computers which helps in
designing mechanical parts or building designs is known as CAD [Computer Aided
Designing]. A design can be viewed from many angles, modified, enlarged or reduced
easily as per convenience. Also computer when specifically
used for engineering purpose,
it is referred as CAE [Computer Aided Engineering].

In Entertainment:

You must be fond of science fiction films, where space battles with space ships
take place and strange looking space creatures fight with each other,
with strange weapons. Many
people who enjoy science fiction are fascinated with the ‘special effects’ that they get to see in these
films. We all know that space ships can’t fly around, strange looking creatures are not be seen

how do film makers man
age to show all this computer generated image of a space ship? This is
done with the help of special effects, generated on computers. Strange looking objects are created
and shown as moving with the help of computers and this process is known as computer

animation. Prior to the computer age, filmmakers used models extensively, but now a day’s
computer graphics are steadily replacing them.

In Communication and Telecommunication:

When a lot of you students hold each other’s hands, you form a

Similarly you can form a ‘computer network’ if you connect different
computers. This can be done with the help of cables, telephone lines and even with
satellites. These connected computers form a computer network. It is increasingly
becoming the basi
s of communications in the World today. Internet is one such global
network, which connects millions of computers throughout the World. It is of a great
help to students, doctors, engineers and to a common man as one can get lot of
information on any top
ic from it. You can also communicate with each other through
electronic mail [E
mail] by which your messages, pictures even sound files can be sent to
any internet user, anywhere in the World with in seconds.

increasing volume of telephone calls are

well handled by the computerized
telephone exchanges which do it very quickly with minimum possible errors. Overseas calls can be
made quickly and directly by means of satellites which otherwise meant slow link
ups between
various operators and switchboa

Desk Top Publishing:

The visiting cards, magazines, newspaper advertisement which you see in daily life are
the creations of Desk Top Publishing [DTP]. DTP is the process of designing and printing done
with the help of computer. Generally the t
erm DTP includes the graphic program like CorelDraw
in which you can create graphics or give wonderful effects to the text and a page lay out program
like PageMaker which is helpful in creating the page layout like making columns, headings,
adjusting graph
ics with in text etc. The final product can be printed on a high quality laser

which can be given for further processing to produce large quantity of printed material.



are used in the library for producing and maintaining
catalogue of the available books. They are also used by the members to search for their
topics in the available books. The computers are also used for maintaining the records
of the members.



are used for reservation of tickets.



are used in flying the aero planes.



are used in offices to handle the routine office work.

Man is the wonder of wonders and (no wonder he) is aiming at the best. Computer is the
result of his ultimate achievements.
Just as human beings are blessed with a brain, computers are a
blessing from human efforts.

The other thing which computer can do is to control functioning of very complicated intelligent
machines like robots satellites etc. In short it can perform the f
unction of calculating sorting,
storing and retrieving data.

It appears that everything can be done through it. Yes it is true that computers can do anything, a
man desires to of, but for making a computer for doing everything you have to invest a lot of
money and mind. One has to be very expert in dealing with computers. But computers of today are
becoming more and more user friendly.




Basically any computer is supposed to carry out four functions:

1. Accepting the dat
a as input.

2. Storing the data and instructions in its memory and recalling the same as and when required

3. Processing the data as per instructions to convert it into useful information.

4. Communicating the information as output.



The data input may be in form of:

(a) Numeric and Different Symbols.

(b) Alphabetic.

(c) Alphanumeric.

Then this is coded into data acceptable to computer in its language. It may be audible,
visual or audiovisual analogic data. In this case, an inter
ing device is required to convert it into
signals which are acceptable to computers.




There lies a history behind everything. Evolution of man has its
own history. The sun, moon and the earth have their own history.
Similarly, there is a history behind the computers as well. This
history shows us the development of the computers through various
stages over thousands of years.

All through the ages, people have done counting and calculations.
The ancient people

used stones for counting. Sometimes they made
scratches on the wall or tied knots in a rope to record information.
But these were very slow ways to get results. People of later ages
were not satisfied with these crude methods. They needed faster m
to do their work. As we know, necessity is the mother of invention.
The discovery of numbers led to the development of all kinds of
calculating devices. Various people have since invented much better
computing devices to do calculations and counting

at a faster speed.
Some of the important computing devices developed from time to time
are described below.


The first calculating device developed and used for
calculations is known to be the Abacus. An abacus consists of beads
on rods.
Moving the beads up and down does addition and subtraction
of numbers.

The Abacus is a simple and an effective manual calculating
device. Even though more than three thousand years old, the Abacus is
still being used in some parts of the world.
Some people are known to
perform the calculations much faster using the Abacus than those using
the modern day electronic calculators.


Blaise Pascal, a young Frenchman, invented
an Adding Machine in 1642. This was a mechanical

calculating device
made from gears, wheels and dials. It was used for adding numbers
quickly. Adding machine based on this principle is still in use.

Jacquards Loom:

Joseph Jacquard, a French weaver, invented an Automated Loom in
1804. Thi
s Loom used punch cards to produce patterns and designs on
cloth. The weaving action of this machine depended on the absence or
presence of holes in the card.

Difference and Analytical Engines:

Charles Babbage
, an English man born in 1833, is known as

the father
of computers. He designed and built a machine called “Difference
Engine". This machine could take in the information and sort it out
in the form of tables. Difference Engine was used to calculate the
logarithm tables accurately. Lady Ada
Lovelace, an associate of
Charles Babbage, developed procedures for solving problems on the
Difference Engine. She is known to be the first programmer of the

Charles Babbage also gave the complete design of a more advanced
calculating machine
called the “Analytical Engine". During Babbage’s
time, the technology was in an advanced state. Therefore, the
Analytical Engine could not be completed.


Hollerith produced cards out of special paper pulp, designed punching
machines to

punch holes in the card to count the figures and invented
sorting machine to read such punched card.



With the discovery of electricity, man started developing calculating devices,
which ran on electricity. The twentieth century had seen a n
umber of such machines.
These machines are capable of performing the calculations at a very high speed without
making mistakes. Moreover, very little effort is required on part of the man to operate
these machines.


"Generation" in computer talk is a step in technology. It provides a
framework for the growth of the computer industry. Originally, the term 'generation' was
used to distinguish between varying hardware t
echnologies. But
now a days
, it has been
extended to include both the hardware and software. Which together make up an entire
computer system.

The custom of referring to the computer era in terms of generation
came into w
ide use only after 1964. There are totally five computer generations known
till today. Each generation has been discussed below in detail along with their
advantages and disadvantages.

Although there is a certain amount of overlapping between the generat
ions, the
approximate dates shown against each are normally accepted.

First Generation (1942

First generation computers used Thermionic valves and programming was done in
machine languages. All the computers were of very big sizes and costly.

n the mid
1940's John von Neumann joined the University of Pennsylvania team,
initiating concepts in computer design that remained central to computer engineering for the next
40 years. Von Neumann designed the Electronic Discrete Variable Automatic Compu
(EDVAC) in 1945 with a memory to hold both a stored program as well as data. This "stored
memory" technique as well as the "conditional control transfer", that allowed the computer to be
stopped at any point and then resumed, allowed for greater versat
ility in computer programming.

First generation computers were characterized by the fact that operating instructions
were made
order for the specific task for which the computer was to be used. Each computer
had a different binary
coded program called

a machine language that told it how to operate. This
made the computer difficult to program and limited its versatility and speed. Other distinctive
features of first generation computers were the use of vacuum tubes (responsible for their breath

size) and magnetic drums for data storage.

"Vacuum tube", which was a fragile glass device that could control and amplify
electronic signals. These vacuum tubes are referred to as first generation computers.


The first electronic computer (El
ectronic Numerical

Integrator And Calculator) was developed by J.P.ECKERT and

J.MAUCHTY in 1946. This was world's first commercial digital

Computer. This machine used vacuum tubes. At the time of its

Development, it was the fastest working machine.

e ENIAC was 30 x 50 feet long, weighed 30 tons, with a cost of $400,000. Today, a
small microcomputer that you can hold in your hand, and costing $10, is many times as powerful
as ENIAC.Yet when ENIAC was built, it was 5000 times faster than the closest co
mpetitor, the
Harvard Mark 1.

The ENIAC had all the modern parts of a computer, such as a central processing unit, memory,
and input/output. The main difference between it and modern machines was that ENIAC used
decimal numbers in its internal operations a
s opposed to modern binary arithmetic.


(Universal Automatic Computer) was the first automatic

Machine used for the business purposes. This machine was evolved

Around 1954.


1. Vacuum tubes were the only electronic components

available during those days.

2. Vacuum tube technology made possible the advent of electronic digital computers.

3. These computers were the fastest calculating devices of their time. They could
perform computations in milliseconds.


1. Too bulky in size

2. Unreliable

3. Thousands of vacuum tubes that were used emitted large amount of heat and burnt
out frequently

4. Air conditioning required

5. Prone to frequent hardware failures

6. Constant maintenance required

7. Nonportable

8. Man
ual assemble of individual components into functioning unit required

9. Commercial production was difficult and costly

10. Limited commercial use

a. The first generation computer control was centralised in a single CPU, and all operations
required a dire
ct intervention of the CPU.

b. Use of ferrite
core main memory was started during this time.

c. Concepts such as use of virtual memory and index register (you will know more about these
terms in advanced courses).

d. Punched cards were used as input dev

e. Magnetic tapes and magnetic drums were used as secondary memory.

f. Binary code or machine language was used for programming.

g. Towards the end due to difficulties encountered in use of machine language as programming
language, the use of symbo
lic language, which is now called assembly language, started.

h. Assembler, a program, which translates assembly language programs to machine language, was

I. Computer was accessible to only one programmer at a time (single user environment).

j. Ad
vent of Von
Neumann architecture.

Second Generation (1955

The transistor, a smaller and more reliable successor to the
vacuum tube, was invented in 1947. However, computers that used transistors were not
d in quantity until over a decade later. The second generation emerged with
transistors being the brain of the computers. With both the first and the

computers, the basic component was a discrete or separate entity.

Many thousands of
individual’s components had to be assembled by hand into
functioning circuits. The manual assembly of the individual

Components and the cost of labour involved at this assembly stage made the
commercial production of these computers difficult and costly.

More sophisticated high
level languages such as COBOL (Common Business
Language) and FORTRAN (Formula Translator) came into common use during this time,
and has expanded to the current day. These languages replaced cryptic binary machine
with words, sentences, and mathematical formulas, making it much easier to
program a computer. New types of careers (programmer, analyst, and computer
systems expert) and the entire software industry began with


Some of the seco
nd generation computers are:

IBM 1620,IBM 1401,IBM 7094,CDC 1604,CDC 3600,RCA 501,UNIVAC 1108 Leo
Mark III, ATLAS, ICL 1901 etc.


1. Smaller in size as compared to first generation computers

2. More reliable

3. Less heat generated

4. These computers were able to reduce computational times from milliseconds to

5. Less prone to hardware failures

6. Better portability

7. Wider commercial use


1. Air
conditioning required

2. Frequent maintenanc
e required

3. Manual assembly of individual components into a functioning unit was required

4. Commercial production was difficult and costly.

Third Generation (1964

Advance in electronics technology continued an
d the advent of
"microelectronics" technology made it possible to integrate large number of circuit
elements into very small (less than 5 mm square) surface of silicon known as "chips".
This new technology was called "integrated circuits" (ICs). The thi
rd generation was
based on IC technology and the computers that were designed with the use of
integrated circuits were called third generation computers.


1. Smaller in size as compared to

previous generation computers.

2. Even more reliable than


3. Even lower heat generated than second generation computers.

4. These computers were able to reduce computational times from microseconds to

5. Maint
enance cost is low because hardware failure is rare.

6. Easily portable.

7. Totally general purpose. Widely used for various commercial applications all over
the world.

8. Less power requirement than previous generation computers.

9. Manual assembly o
f individual components into a functioning unit not required. So
human labour and cost involved at assembly stage rescued drastically.

10. Commercial production was easier and cheaper.


1. Air
conditioning required in many cases.

Highly sophisticated technology required for the manufacture of IC chips.

Fourth Generation (1975 ONWARDS):

Initially, the integrated circuits contained only about ten to twenty
components. This technology was named

integration (SSI). Later, with the
advancement in technology for manufacturing ICs, it became possible to integrate upto a hundred
components on a single chip. This technology came to be known as medium scale integration
(MSI). Then came to the

era of large scale integration (LSI).

When it was possible to integrate over 30,000 components onto a single chip. Effort is
still on for further miniaturization and it is expected that more than one million
components will be integrated on a single chip

known as very large scale integration

A fourth generation computer, which is what we have now, has LSI
chips as its brain. It is LSI technology, which has led to the development of very small
but extremely powerf
ul computers. It was the start of a social revolution. A whole
computer circuit was soon available on a single chip, the size of a postage stamp.
Overnight computers became incredibly compact. They became inexpensive to make
and suddenly it became poss
ible for anyone and every one to own a computer.


1. Smallest in size because of high components density.

2. Very reliable.

3. Heat generated is negligible.

4. No air conditioning required in most cases.

5. Much faster in computati
on than previous generations.

6. Hardware failure is negligible and hence minimal maintenance is required.

7. Easily portable because of their small size.

8. Totally general purpose.

9. Minimal labour and cost involved at assembly stage.

10. Cheapest
among all generations.


Highly sophisticated technology required for the manufacture of LSI

Fifth Generation (YET TO COME):

Scientists are now at work on the fifth generat
ion computers

promise, but not yet a reality. They aim to bring us machines with genuine I.Q., the
ability to reason logically, and with real knowledge of the World. Thus, unlike the last
four generations, which naturally followed its predecessors, t
he fifth generation will be
totally different, totally novel, and totally new.

In structure it will be parallel (the present ones are serial) and will be able to do
multiply tasks simultaneously. In functions, it will not be algorithmic (step by step, wi
one step at a time). In nature, it will not do just data processing (number crunching) but
knowledge preceding. In inference, it will not be merely deductive, but also inductive.
In application, it will behave like an expert. In programming, it will

interact with humans
in ordinary language (unlike BASIC, COBOL, FORTRAN, etc. Which present computers
need)? And in architecture, it will have KIPS (Knowledge Information Preceding
System) rather than the present DIPS/LIPS (Data/Logic Information proces
sing System).

The odds of coming out with a fifth generation computer are heaviest for Japan.
They have already started work in this direction few years back. Japan has chosen the
PROLOG (Programming in Logic) language as its operating softwar
e and plans to have
the final machine talk with human beings, see and deliver and hear the normal, natural




1. Speed:


computer is a very fast device. It can perform in a few
seconds the amount of
work that a human being can do in an entire year

if he worked day and night and did
nothing else. To put it in a different manner a computer does in one minute what would take
a man his entire

A powerful computer is ca
pable of performing about 3 to 4 million simple arithmetic operations
per second.
A computer has a tremendous speed to work on huge amount of data to produce
100percent accurate results. For us, a second is very fast but for a computer a second is too lo
ng a
period. It works in Millie, Micro, Nano and Pico seconds. The table belong shows the relationship
between a second and the terms just mentioned.

From it, you will realise how fast a computer works.

Units of time

Part of a second

Millie second [ms

One thousandth [1/1000]

Micro second [us]

One millionth [1/1000,000]

Nano second [ns]

One billionth [1/1,000,000,000]

Pico second [ps]

One trillionth [1/1,000,000,000,000]

How does a computer work so fast?

A computer has electronic circuits insid
e it and all its operations are performed in the
form of electrical signals, which travel at incredible speed, which results in its high speed.

2. Accuracy:


accuracy of a computer is consistently high and the degree of accuracy of a
particular compu
ter depends upon its design. But for a particular computer, each and every
calculation is performed with the same accuracy.
It is composed of electronic circuits, which
performs millions of instructions in a second to give us accurate results. In

case a
ny wrong results
are delivered, we should straightaway check for erroneous data or wrong instructions. For
example, if you are expecting the result 5 and giving the data and the instructions like 10
4 or
10+5, there is no use of losing your temper on the
computer, you have given just the wrong input.

Remember it works on the principle of GIGO, i.e. Garbage In Garbage Out. It means, if
you input the faulty data or instructions, you are bound to get the wrong results.

3. Diligence:


human beings,
a computer is free from monotony, tiredness, lack
of concentration etc., and hence can work for hours together without creating any error
and without grumbling. Due to this property, computers obviously score over human
beings in doing routine type of job
s, which require great accuracy. If 10million
calculations have to be performed, a computer will perform the 10millionth calculations
with exactly the same accuracy and speed as the first.

4. Versatility:


is one of the most wonderful featu
res of the computer.
One moment, it is preparing the results of particular examination, the next moment
it is busy preparing electricity bill and in between, it may be helping an office secret
to trace an important letter in seconds. All that is required

to change its talent is to
slip in a new program [a sequence of instructions for the computers] into it. Briefly,
a computer is capable of performing almost any task provided that the task can be
reduced to a series of logical Steps.


We human beings have a limited memory. Remembering huge amount of data as
contained in a telephone directory is beyond our capacity. Storing this kind of enormous data on
paper will generate problems of maintenance and make it difficult to look

for a particular record.
However, with the help of computers, we can store any amount of records of an organization in a
particular sorted way and get any details with in seconds out of huge number of stored records.

6. NO I.Q.:

A computer

is not a magical device. It can only perform tasks that a human being can. The
difference is that it performs these tasks with unthinkable speed and accuracy. It possesses no
intelligence of its own. Its I.Q. is zero, at least till today. It has to b
e told what to do and in what
sequence. Hence, only the user can determine what tasks a computer will perform. A computer
cannot take its own decision in this regard.


Computers are devoid of emotions. They have no f
eelings and no instincts because they
are machine. Although men have succeeded in building a memory for the computer, but no
computer possesses the equivalent of a human heart and soul. Based on our feelings, taste,
knowledge, and experience, we often ma
ke certain judgments in our day
day life. But
computers cannot make such judgments on their own. Their judgment is based on the instructions
given to them in the form of programs that are written by us. They are only as good as man make
and uses them




Computers have mainly four categories:

1. Digital

2. Analog

3. Hybrid

4. Optical

There are two main classes of computers:

Digital and Analogue.

1. Digital Computers:

a. Digital computers operate by numerical

counting (adding) of discrete data, using the method of
controlled arithmetic operations.

b. Digital computer represents the data into digits and then all operations are done on these digits
at extremely fast rates.

c. Digital computer basically knows
how to counts the digits.

d. Digital computers employ many interchangeable arithmetic devices in usually sequential
operation. Hence, cost is relatively high and programming is complex.

Digital computers have been grouped into four main classes:

Micro Computers

2. Mini Computer

3. Mainframe Computers

4. Super Computers

(1) Micro computers:

A microcomputer is a computer who’s CPU is a microprocessor. A microprocessor is a processor all of
whose components are on a single integrated
it chip.

Home computers, personal office computers are examples of microcomputers, which have proliferated
bringing, computing power and literacy to more and more people. In terms of number of units,
microcomputers are those of all other types of compute
rs combined.

Microcomputers can be sub
divided into two types:

(a) Home Computer:

Home computers are meant for hobbyists rather than professionals. These consist of a keyboard
integrated with CPU in one box type thing and interfaced with ordinary tel
evision and
They are meant for entertainment, and training. Vendors supply cassette tapes containing programs
for computer games and for entertainment. Some popular home computers were D (
81, Sinclair's
Spectrum, Tandy's TRS
80, Atari 40
0 and IBM's PC Junior etc..

of India is producing a
computer known as SCL
Uniform, for massive computer illiteracy project for Indian schools. This
project is known as CLASS (Computer Literacy And Studies in Schools) project.

(b) Personal C

Personal computers are called so because they are designed for personal use of individual or individual
small business. They are meant for professionals, small business units and office automation systems.

PC can be used for a variety of app
lications like: Computer literacy, BASIC Programming, Fun and
Games, Home and School applications, Business and Professional applications, Electronic spread
sheets, Telecommunications, Data Base Management, Accounting, Word Processing.

(2) Minicomputers

By early 1960, economic and technical factors combined to make small, inexpensive computers
attractive for many applications. Many computing tasks could be accomplished with less power than
was then available on the contemporary mainframe computers. T
his led to the advent of
minicomputers. Throughout the 1960s and 1970s advances in technology led to the increasing
functionality of the minicomputer. Speed of execution, memory size, and other characteristics of
minicomputers increased with advances in t
echnology. The availability of low cost memory allowed a
dramatic increase on the size of main memory attached to the minicomputers.

(3) Main Frame Computers:

Although there has been some blurring of the boundaries between minicomputers and mainfra
computers, the mainframe remain a distinct class of computers.

There are some key differences between the mainframe class computers and the mini class computers.
One of the most dramatic differences is in the speed of the two classes. A common measur
e of speed is
Million of Instructions Per Second (MIPS); this is the rate at which machine instructions are executed.
An IBM 3090/600 is rated at 102 MIPS whereas VAX 8842 is rated at 22 MIPS. It is sometimes
dangerous to compare MIPS rating of dissimilar

machineries, since the typical instruction on one
machine might do more than the typical instruction on another. However, the instruction sets of
mainframes and super computers are comparable, so this is a fair comparison. Another dramatic
difference is i
n price. An IBM 3090/600 model would have costed

around $ 12.4 million in 1988.

In terms of dollar volume, mainframe are the largest sector of the computer hardware market, and the

continuous to grow. The question might arise, why such exp
ensive machines continue to
survive on the world of microcomputers and low cost minis. The primary function of mainframes
today is to support large databases. Large business and government organizations need a central
repository of data that can be manage
d and controlled centrally. Only the mainframe has the
processing power to handle large database systems. Moreover mainframes have more that kept up
with other classes of computer in terms of price and performance.

(4) Supercomputers:

Although the pe
rformance of mainframe general
purpose computers continues to improve
relentlessly, there remain applications that are beyond the theoretical performance limits of the
contemporary mainframe. There is a need for computers to solve multi variate mathematica
problems of real physical processes, such as occur in disciplines including aerodynamics, seismology,
metrology, and atomic, nuclear and plasma physics. Typically, these problems are characterized by
the need for high precision and a program that perform
s floating point.

Arithmetic operations on large array of numbers. Most of these operations fall into the category
known as continues field simulation.

To handle these types of problems, the supercomputers has been developed. These machines are
lly capable of handling hundreds of Millions of Floating point Operations Per Second
(MFLOPS) and cost in the 15
20 million
dollar range. Although a supercomputer is capable of general
purpose applications found on mainframes, it is optimized for the type
of numerical calculation
involving arrays.

The Super computer has limited use because of its price tag, a limited market. Only these machines are
used for operational in India, mostly at research centers and some government agencies with scientific
or e
ngineering functions. As with other areas of computer technology, there is a content demand to
increase the performance of the supercomputer. In some current applications in aero dynamics and
nuclear physics, as many as arithmetic operations, requiring mor
e than two days of computing time on
a contemporary supercomputer, are needed for a single problem. Thus the technology and
performance of supercomputer continues to evolve.

computers are able to reach the large volume and speed performances far be
yond the
theoretical limits of main
frames by using parallel processing, vector processing and pipelining
techniques. These techniques are beyond the scope.

2. Analogue Computers:

a. Analogue computers are mostly used in engineering and scientific calcu

b. Analogue computers employee relatively few distinct, single
purpose devices in parallel
operation. Hence, cost is relatively low and programming is easy.

Comparison of the Analog and Digital Computer:

The accuracy of analogue compu
ters is limited to the accuracy of digital computers, is
essentially unlimited. Analogue computers are best suited for simulating the response of physical
systems, while digital computers are best suited for handling numerical problems, statistical data,
and discrete random process. Digital computers can be set up, however, to serve as mathematical
models of physical systems.

3. Hybrid Computers:

There is another category of computers, which should be mentioned in passing. These are the
hybrid compute
rs, which make use of both analogue and digital components and techniques. The
car speedometer may be considering a hybrid, although it does not employ true digital techniques.
The digital differential analyzer is a true hybrid, since it uses digital cir
cuits and techniques in
machine that is organized like, and the purpose of an analogue computer. The most recent
analogue computers use digital memory storage for intermediate results or repetitive problems;
other hybrid exist. To use both types of comput
ing techniques for solving a problem, 'analogue
digital' and 'digital
analogue' converters are required, which will make analogue data palatable
to a digital computer, and vice versa.

Hybrid computers make use of both analogue and digital techniques
. They employ analogue
digital and digital
analogue converters for transforming the data into suitable form for either
type of computation.

4. Optical computer:

Optical computers will be super high speed computer yet to be developed which shall
ork on quadru system logic.



I (a) Questions

Q.1. What is a general
purpose machine?

Ans. A machine, which can be used for variety of applications and is not modeled only for specific
s. Von Neumann machines are general
purpose machines since they can be
programmed for any general application, while a microprocessor based control systems are not
purpose machines as they are specifically modeled as control systems.

Q.2. List the

advantages of IC technology over discrete components.

Ans. Low cost

(a) Increased operating speed

(b) Reduction in size of the computers

(c) Reduction in power and cooling requirements

(d) More reliable

Q.3. What is a family of computer? What are its cha

Ans. A family of computers is a set of compatible models, which have the characteristics such as
Similar instruction sets and operating system z increase in execution speed,

ports, memory from
lower to higher member of family z higher cos
t of each successive member.

Q4. Define the following terms briefly:

(1) Microprocessors

(2) Laptop

(3) Supercomputer

Ans. (I) Microprocessor is a complete processor constructed on a single chip using VLSI
technology. Intel and Motorola are two popular Mi
croprocessors. (ii) A very small, battery
operated microcomputer, which uses liquid crystal display technology and very handy to carry.
(iii) The upper end of the state
art mainframe machines. Very powerful computational
capabilities. Mainly suitable fo
r very large processing requirements such as weather forecasting.

Q.5 Briefly describe the difference between a digital and an analog computer, and give an example
of each.

Ans. A digital computer, such as a hand or desk calculator, represents data in ter
ms of discrete
numbers, whereas an analog computer represents data in terms of some continuous physical
quantity. A household thermostat is an elementary analog computer.

Q.6. What are the three types of computers? How do they differ?

Ans. Analog, digital

and hybrid. Analog computers simulate continuous, physical processes by
measuring analogous electrical signals. Digital computers deal with discrete, instead of continuous
quantities. They count instead of measure. Hybrid computers combine the characteris
tics of
analog and digital computers.

Q.7. What event prompted many manufacturers to enter the microcomputer market?

Ans. IBM introduced the 16
bit IBM PC 20 A computer, keyboard, monitor, one or two disk
drives, and a printer.

Q.8. What basic equipment
makes up a fairly versatile microcomputer system?

Ans. They are A computer, keyboard, monitor, one or two disk drives, and a printer.

Q.9. What features make portable computers useful to salespersons?

Ans. They are lightweight, flat, easy to carry, and do

not need an external source of electricity.

Q. 10. Compare microcomputers with minicomputers and mainframes in terms of size, cost, and

Ans.They are smaller, less expensive, and have lesser capabilities, although some approach

in capabilities.

Part I (b) Objective Type Questions with Answers

A1. Choose best possible alternative from following

1. The very small and cheap computer built in to many home devices is called ___ computer.

(a) Main frame

(b) Mini

(c) Micro

(d) Analo

2. The main distinguishing features of fifth generation digital computers will be

(a) Liberal use of microprocessors

(b) Artificial intelligence

(c) Extremely low cost

(d) Versatility

3. The 68000 series of Microprocessor are from

(a) DEC


(c) H

(d) None of the above

4. PARAM is a

(a) DBMS package

(b) Parallel Computer

(c) Programming Language

(d) Parallel Random access memory

5. One computer that is not considered a portable computer is

(a) Minicomputer

(b) Laptop computer

(c) Notebook compute

(d) None of the above

6. The unit of speed used for super computer is




(d) None of the above

B1 Fill in the blanks with appropriate word(s)

(a) Word processor is also a ___ computer.

(b) Hybrid computer is a combination o
f ___ and ___ computers.

(c) ___ are the devices, which convert analog signals into digital.

(d) Microcomputer belongs to ___ generation.

(e) The super computers of ___ generation will have thinking power also.

(f) ___ Invented analog computer.

B2. Fill i
n the blanks:

(a) ___ is the world's fastest computer.

(b) Mini computer is ___ than midi or super computer.

(c) Microcomputer is the computer belonging to ___ generation.

(d) ___ Computer is used for making documents in offices.

(e) The computer known as

___ can process several Indian languages.

(f) The name of computer approved by NCERT for mass computer literacy project is ___.

(g) ___ Computer is 100% accurate.

(h) The accuracy of ___ computer is little poor.

(i) Robots are good example of ___ computer

C1. Decide in case of each one of the following statements whether it is True or False?

(a) Mini computer is also called a mainframe computer.

(b) Personal computers are the most popular computers.

(c) Microcomputer is faster than minicomputer.

(d) Opt
ical computers are going to be the super fast computer.

(e) Analog computer is called 99% accurate computer.

(f) Microcomputer is called micro because it consists of microprocessor.

C2. State whether True or False.

(a) Mini computers are the fastest comp

(b) Some of the super computers can process 64 instructions at the same time.

(c) Personal computer is the most popular computer.

(d) Personal computer is not a microcomputer.

(e) SCL's Unicorn computer is a microcomputer manufactured in India.

Micro computer is the faster computer than mini computer.

(g) Analog computer is a mixture of hybrid and digital computer.

(h) Digital computer knows only how to add.

(I) Odometer is a digital type mechanical computer.

(j) BBC's 'Micro' is an educational c

C3. State in case of each of following statement whether it is true or false?

(a) C
DOT manufactures computers.

(b) The first electronic computer used transistors.

(c) The first electronic computer was ENIAC.

(d) Digital computers running on ele
ctronic valves (vacuum tubes) are known as first

(e) Third generation computers use VLSI chips for both CPU and memory.

(f) Fifth
generation computers are under developmental stage.

(g) Second generation computers were knowledge based

(h) Hybrid computer is a mixture of both digital and analog computers.

(I) Microcomputer is called micro because it consists of micro


(j) Personal Computer is a microcomputer.

(k) PARAM is a super computer.

(l) Personal Computers use multiple


(m) In analog computers the output is converted from digital to analog form.

(n) Minicomputers are faster and more powerful than microcomputers.

(o) Mainframe computers are slower than minicomputers.

(p) The cycle time of a supercomputer may b
e as low as 4 nanoseconds.

(q) CRAY3, which is designed with 16 processors, is 100 times faster than CRAY2.

(r) The Processing speed of the supercomputer lies in the range of 400 MIPS

10,000 MIPS.

(s) Supercomputers are not yet manufactured in India.


1. (c) 2. (b) 3. (d) 4. (b) 5. (a) 6. (c)

B1. (a) Micro (b) Analog, Digital (c) Moderns (d) Fourth (e) Fifth.

B2. (a) NEC's SX
2 (b) Smaller or slower (c) Fourth (d) Word processor (e) Sidhartha or Lipi (f)
SCLs Unicorn (g) Digital (h) Analog (i) Hyb

C1. (a) False (b) True (c) False (d) Fourth (e) Fifth.

C2. (a) False (b) True. (c) True (d) False (e) True (f) False (g) True (h) True (i) False (j) True.

C3. (a) f (b) f (c) t (d) t (e) f (f) t (g) f (h) t (i) t (j) t (k) t (l) f (m) f (n) t (o) f (p
) t (q) f (r) t (s) f


1. What are the four different types of computers size wise?

2. How is super computer different from other mainframe computers?

3. What are the different types of microcomputers?

4. What are the advantages
of using mini computer over microcomputer?

5. How is the microcomputer different from other computers?

6. What are the four different types of computers based on their working methods?

7. Write down the name of at least three computers of each category siz
e wise.

8. Distinguish between

(a) Chip and integrated circuit.

(b) Integrated circuit and microprocessor.

(c) Microprocessor and microcomputer.

(d) Analog and digital computer.

(e) Valve and Transistor.

(f) Mainframe, mini and microcomputer.

(g) Computer
and calculator.

9. For what purposes might you use a supercomputer? Have you heard of any uses other than the
ones mentioned in the text? What are they?

10. What market trend currently is affecting sales of minicomputers?

11. (a) give three examples of pc
systems used primarily in the home.

(b) What are three examples of professional pc models?

12. (a) what is a minicomputer?

(b) How may minis be used?

13.(a) what is a mainframe computer?

(b) How may mainframes be used?

14. Give four examples of representat

(a) minicomputers and

(b) mainframe computers.

15. Identify and discuss three characteristics of

(a) minicomputers,

(b) mainframe computers, and

(c) supercomputer.

16.(a) What is a super

(b) How does a super
computer differ from other machine

(c) How are supercomputers used?




1. Input devices

2. Output devices

3. Processing unit

4. Memory

As is clear from the functioning of the computer, you need input devices to give
the input and the CPU to process the

data and the output devices to display the results. Let us
understand these devices in detail.

Input Device:

A device whose purpose is to allow the user to provide input or information to
a computer system is called an Input device.

Input de
vices are those devices that we use to send information into the

Input is the process by which you communicate with your computer. Usually
this is accomplished by using a mouse, keyboard, Braille display, microphone or another
device that allow
s you to give information to the computer.

The following are the various input devices:


All of you must have worked on a keyboard. It is an integral part of a computer. Just
like we feed ourselves with our hand, which is made up of five dif
ferent types of fingers, we feed
the data into the computer with different types of keys present on the keyboard.

The keys can be classified as follows:

1. Alphabetic keys

2. Numeric keys.

3. Function keys.

4. Special keys.

5. Cursor control keys.

abetical keys:

These are used to input the alpha


2. Numeric keys and numeric keypad:

These are used to input numeric data.

3. Function keys:

These keys are used to perform some specific functions. Like F1 is used to
get help.

4. Spe
cial keys:

Enter/Return key:

Accepts the current entry or command.

Shift key:

Prints signs and upper/lower case letters [depending upon whether the Cap slog
is on or off].

Caps Lock key:

Enable/disable upper case characters.

Backspace key:

letes the characters to the left of the cursor.

Tab key:

It moves the cursor from one cell to another or from one entry field to another.

Delete key:

It arises the character to the right of the cursor.

Escape key:

It cancels the current operation

Alt and Ctrl keys:

these keys are used with other key to make various combinations of keys.
For example, Alt+F will open the file menu in MS word and other window based programs.

5. Cursor control keys:

These four keys navigate the cursor in all f
our directions.

How does the key board work?

When a key is pressed, the keyboard controller [small computer chip] generates a code
called the key’s scan code and this code is received by the CPU and interpreted to the key

Remember the keyboar
d, which is used with a PC, is a QWERTY keyboard. It gets its
name from the arrangement of its alphabetic keys.

MOUSE: A Mouse is used with a graphical interface l
ke windows based software. When you
move a Mouse on a flat surface [a Mouse pad], The
pointer moves on the screen. You can
‘click’, ‘double click’ or ‘drag’ the Mouse, to perform various operations. A Mouse has a ball
inside, which touches the surface of Mouse pad. As the Mouse is moved, the ball also moves.
There are two rollers inside

the Mouse, which are also rotated by the movement of ball. This
movement translated into the electrical pulses and sent to the computer, which detects and
changes the movement into X and Y co

Remember when your Mouse starts misbehaving, lik
e the pointer gets struck or jumps
from one place to another on the screen instead of moving smoothly, it means that dust has
accumulated on the rollers and cleaning is needed. This is the time when you should get the
Mouse cleaned.


A Joyst
ick is a stick, which is mounted on a spherical ball, and moves left or right,
forward or backward in a socket. By moving Joystick you can move the cursor on the screen.
Joysticks are mainly used to play games in the computer.

Image Scanners:

First of

all, let us understand what do we mean by scanning? Scanning is
the process of digitizing a document [text or pictures] so that it can be entered into the
computer. A Scanner is used to capture images, pictures, photographic prints etc. In the
d former so that these can be inserted into your computer styles and can also be edited
and formatted to give various effects.

The Types of Scanners:

We have two major types of scanners

Flatbed scanners.

2. Hand held scanners.

The Flatbed scanner:

In a Flatbed scanner, you place the document on the flat scanning
surface and the scanning takes place with the help of a light source which illuminates the
paper and the light of different magnitudes is reflected from the dark inked areas or the
blank are
as on a scanning mechanism. This light is converted into electrical signals and
further into dots, which are sent to the computer for storage.

Remember you can have these scanners available in different paper sizes like A4 or
A3 and also of different re

The Hand Held Scanners:

A hand hel

scanners is held in the hand and is moved slowly, at a
constant speed along the length of the document. The scanning process takes place while the
scanner is being passed over the document. These scanners

are cheaper than the flatbed
scanners and can scan documents of limited width and height. To scan large documents, you
need to have multiple passes and then combine them.

Remember you can have gray scale or coloured scanners of different resolutions.


Microphone is used for the sound input. A sound card is also
necessary to translate the electrical signal from the microphone into a digitized form
that the computer can store and process.

Optical Character Reader [OCR]:

Optical reade
rs can accept and convert the hand
written or printed matter as the computer data. Earlier OCR used to recognize
printed type machine
readable fonts. The common fonts used for such purposes are
A fonts, which originated in USA and OCR
B fonts, which
originated in

Remember OCRs
, which read the hand written, and other printed characters
although different or illegible handwritings produce a higher error rate. However it
is a good alternative to entering data using the keyboard.

Optical Char
acter Recognition [OCR] process:

If you have scanned the text, you
can use the OCR software so that the image can be converted into text or editing.
The OCR process starts with the photo scanning of the image into the character
code, so that it beco
available for storing and editing.

Remember the big libraries to are using OCR process digitized and preserve
their holdings. It is of great help in publishing and printing departments where lots
of text is processed daily.

How does the OCR process
take place?

First, the OCR software tries to match each character against the already stored
templates and the closest match is accepted.

2. Then an attempt is made to recognize the unidentified characters by observing the
height, lines and curve … of
the character. This is called feature extraction.

3. The characters still unidentified are tried to be recognized by using the contextual
analysis where guesses are made by seeing the construction and the placement of
characters. For examp
le, if a word l
ooks like “proces
s”, it is changed to “process”
since it is unlikely for a number to come between two characters in a word … in this
way the finished document can be saved in the computer.

Magnetic Ink Character Recognition [MICR]:

This input device i
s used to read the cheque
numbers from a cheque directly without the need to enter the data manually into the computer. It
makes processing faster and the chances of human error or delay involved in reading the cheque
details are eliminated. You must hav
e seen the numbers return on cheques in a special way.
These are printed with a special type of ink containing magnetized iron oxide. These numbers are
recognized by the Magnetic Ink Character Reader device to get the required input. There are two
tic fonts used for processing the cheques. The first one is the E
13 B font, which consists of
10 numbers [0
9] and four symbols. This font has its rotes in the USA another font CMC7, which
originated from France and is commonly used in Europe, includes
numbers [0
9], alphabets [a to
z] and 5 special symbols. These symbols in each font help to store information about the bank
code, the branch code, the account number and more …

Light Pens:

Light pen is a pointing device, which consists of a photocell

put inside a small tube.
When it is moved over the screen, the light coming from the tip of the pen is detected and an
appropriate action is taken. It can be used to choose a menu option or directly draw on the screen
while working in a program like Com
puter Aided Designing [CAD] or inputting messages or
signatures, which are to be stored and sent as graphic images, or in a fax.

Touch Screen:

Touch screen is a computer display screen, which respond to the human touch. A
user gives command by touchin
g the pictures, the icons or the words on the screen with his figures
instead of typing the commands or using the mouse to point and click on them.

The available
hardware and software detect the location of touch and respond accordingly.

Remember th
e Touch screen can be used in home automation systems, restaurant systems,
gaming systems, public information systems where users can query for information without any
prior computer knowledge and for the physically disabled people who cannot use the keybo
ard or
the mouse.

Bar Code Readers:

You must have seen thick and thin black bars on many products in a super
market or departmental stores. Infact you can find it on all most all the standard products like
books, courier packs, consumer goods in super
market … These codes identify the product,
manufacturer and its price as well. The most commonly seen bar code is the Universal Product
Code [UPC]. A bar code reader is the device which is used to read the bar coded data. You can
have hand held bar cod
e readers or flat bed type bar code readers. These bar code readers project
the laser beam over the bar code and the light sensitive detector identifies the pattern of coding
from the reflected light to convert the individual bar patterns into numeric dig
its. These numeric
digits are just like once typed from the keyboard and passed on to the CPU for further actions.

Remember the Bar Code Readers are also a type of optical image scanners because they
also convert the image of the bar codes in an electron
ic form.

Digital Camera:

The digital camera records and stores images shot in digital format. So that this can be
directly down loaded into a computer. In a digital camera photos can be stored on 3.5 inches
floppy disk, smart media or on compact fl
ash storage cards. Currently, Kodak, Canon, Sony and
several other companies manufacture digital cameras.

Advantages of Digital Camera:

Pictures can be viewed immediately after they are taken.

2. Images not required can be deleted and retaken.


Pictures can be easily outputted in many different ways

printed, can be put on a website or E

Functions of Input Unit

Input unit is actually a device which provides man to machine
communication with computer. Input of any form is first convert
ed into
binary electronic signals, which can be understood by central processing
unit. This process is called digitizing. Input data may be linguistic,
mechanical, graphical, audio, visual or audio
visual. Linguistic input
means a written program in comput
er's programming language which is
inputted to computer either by typing on its keyboard, or by punched
card or by some recorded means like floppy disk, magnetic tape or
cassettes. Audio input is given to computer through voice.

Output Devices: Output dev
ices are those devices that a computer uses to give information to us.

Types of output devices:


Monitor: It is also called a visual display unit. It is a device like a small television. The
size of the monitor is normally measured from the top left c
orner to the bottom right corner of the
display area of monitor. Normally 14" or 15" monitors are used with the PC's. 17" or 19"
monitors are also available. It can either be coloured or black and white. The black and white
monitor is called monochrome mon

Most of the monitors used Cathode Ray Tube Technology [CRT] the same as used in the
television. The screen surface, which is coated with phosphorus, emits a dot of light when struck
by electron beam from electron gun enclosed at the end of the vac
uum tube. In colour system, 3
different electron beams one each for red, blue and green are used.

Remember the screen images are repeated at the refresh rate as the image dissipates


Printer: Printer is the device that prints the text or grap
hics on a paper. Information is
stored on the computer. This information can be printed on a paper using this device. We can get
the print out in Braille if the printer is a Braille printer. The printers can be classified into two
types: Impact printers, N
impact printers.

The printers that fall into the category of Impact Printers are:

Daisy Wheel Printer: This printer uses the technology similar to the electronic typewriters.
Typeface of all the characters is present in a wheel by which this printer
gets its name.

Chain Printer: These are the printers, which have typeface of all the characters in a chain, and
printing is done by hitting of hammers against the characters of the chain.

matrix Printer: It is a commonly used printer. Each alphabet i
s formed by a matrix of 9 or 24

All the above
mentioned printers use carbon ribbons for printing.

The printers that fall into the category of Non
impact Printers are:

DeskJet Printer: In these printers the liquid ink is sprayed on the paper using
a fine nossel, which
provide extremely flexible font variations and graphic printing capabilities to this printer.

Laser Printer: The toner of this printer is in the form of powder. Burning of the images using a
laser forms the characters. These images ar
e then transferred on to the paper from the drum.


Speakers: They provide sound output from the computer. The speakers are connected to
the sound card, which is installed inside the system box.

To get the sound output, you need to attach speakers your

The speakers, which are attached to your computer, are similar to those attached with
the stereo. They are just smaller and also contain their own small amplifiers.

The mechanism of speakers:

The sound card in your computer which is actuall
responsible for producing sound, converts digital sound into electric current, which is ultimately
responsible for the reproduction of sound through the speakers.

D. Plotters:

When the size of a drawing is very large. We use plotter to print the draw
Plotters are commonly used in case of engineering designs. A plotter has multiple pens, which are
moved by the access arm according to the instructions given by the computer. As per the
instructions the appropriate pen is picked up and placed at th
e acquired co
ordinates on paper
and a line is drawn to the end point.

We can have Flat bed type and Drum type plotters.

Flat Bed Type Plotters:

Here the paper does not move but the pen holding mechanism (different
coloured pens mounted and a carriage
) has to provide all the movements of pens.

Drum Type Plotters:

Here, the paper is wrapped around the drum which rotates back and forth
to produce an up down motion. The rest of the movements of the pens across the width of the
paper are the same of in

case of flat bed plotters.

Functions of Output Units:

The output coming from the CPU is in the form of
electronic binary signals which needs conversion in some form
which can be easily understood by human beings i.e. graphical,
alphanumeric in human
language, audio and visual. This function
is performed by Output Units. When the data has been processed
by CPU and converted into information, the results are in the
form of electronic signals. Output unit converts them into a
form, which could be easi
ly understood by us. The output can be

(1) On the screen of the visual display unit

(2) In printed form by printers

(3) In graphic form by plotters


Processing Unit:

Processing includes mathematical operations like add
ition, subtraction,
multiplication and division. Processing also include logical functions like comparison and sorting.

Central Processing Unit (CPU) of a computer resides in the system box. Physically, there are
processor chips, which are plugged on a ci
rcuit board called the motherboard. The most important
processor chip is the microprocessor chip. 386, 486, Pentium etc are the names of various models
of microprocessor chip.

CPU is responsible for receiving the instructions, processing them and
g the results to the output units.

The functions of a CPU are:

(a) To access and store relevant data and instructions during

(b) To control the sequence of operations.

(c) To give commands to, and coordinate the actions of all parts of the

computer system.

(d) To carry out

Central Processing Unit consists of the following components:


Arithmetic and Logical Unit [ALU]

B. Control Unit [CU]

C. Memory

a. Arithmetic and Logic Unit:


ALU consists of high
speed memory locati
ons directly built into the CPU. It is responsible for the
arithmetic [+,
, *, /] and logical operators [<, >, <=, >=, <>] on the data entered.

Control Unit [CU]:

CU does not process or stored data but maintains the flow of data between the ALU, Memo
ry and
the Input/Output devices. Some times, it just transfers the data from the memory to the output
devices or to the storage devices. But if it finds the instructions for the arithmetic or logical
operations, it transfers them to ALU for further proce


The memory or the primary storage stores the data before processing, intermediate
results, and the final results obtained after processing, in different storage sections. The programs
or instructions given for the processing are also sto
red here.

Computer has many types of storage devices. These devices can be classified
into two categories: Primary memory and Secondary memory.

Primary Memory:

Primary memory devices are in the form of a computer chip. These memory
chips are plugged on

the motherboard. In a PC, there are four types of primary memory

Random Access Memory (RAM)

This is the main memory of the computer. This is the working
memory. Any programme or data first gets transferred to this memory and then only user can u
them. Any thing that is typed on the keyboard goes on to the RAM. Any thing that is displayed on
the screen comes from the RAM. RAM is volatile memory. As soon as electricity is switched off,
RAM becomes blank.

Read Only memory (ROM)

The name of th
is memory suggests that you can only read
from this chip and cannot write or change any thing on it. It is similar to a printed book that you
buy from the market. You only read from the book and do not write any thing on it yourself. This
chip contains imp
ortant information and instruction to enable a computer to startup and identify
various components with in the computer. ROM is non
volatile memory. That is, even in the
absence of electricity, content of this memory is not lost.

There are two types of Re
ad Only Memory [ROM]:

a. P R O M [programmable read only memory]:

Here you can write information only once. From then onwards you can only read from it.

b. E P R O M [erasable programmable read only memory]:

Here you can write to in it and erase it by sp
ecial ultra violet radiation and write new programs
into it.

Cache Memory

This memory resides between RAM and the processor. This memory
can be accessed at a very fast speed. It temporarily holds the data, which is sent or received from
the processor.
The objective of this memory is to increase the working speed of the computer. If
Cache memory is a part of the microprocessor chip then it is called Level 1 cache or onboard cache
or l1 cache. If Cache memory is installed as a separate chip then it is cal
led level 2 cache or l2
cache. Cache Memory is also a volatile memory.


this is the memory that holds the data while it is being processed. This
memory is a part of the microprocessor chip. Registers are also volatile memory.

Secondary Memory

Secondary memory consists of different storage devices in
which you can store the work done on the computer.

The popular storage devices are floppy disks, magnetic tapes, hard disks and
CD ROMs. Although all of these are storage devices more over th
ey differ from each
other in many ways. In the case of a floppy disk, you can easily write on it. Its
capacity is however less but it has the advantage of being portable [easy to be carried
any where]. The hard disk on the other hand has a large capacit
y and is fixed in side
the CPU. It is very easy to write and rewrite on the hard disks and floppy disks.

Remember we also have optical storage devices like compact disks, which have
huge capacity, but they need special equipments to write on.


Let us take a look at the different types of storage devices we commonly use.

Floppy Disks:

Despite the increasing capacity of the hard disks and evolution of new
storage mediums, the use of floppy diskettes is still very popula
r. Earlier in the
1980’s most of the PCs used 5.25inches floppy disks of the capacity 360KB or 1.2MB.
However, these were prone to get damage very easily due to dust or bending. Now
the 3.5inches floppy diskettes are becoming very popular because of the
ir rigidity and
larger storage capacities. You can see the different portions of a floppy diskette as

The disk inside the square plastic protector is coated with iron oxide. The more
the density of the diskette, the more tightly packed are iron o
xide particles. These
diskettes evolved from lower to higher density as shown.




5.25 inches

Double density

360 KB

5.25 inches

High density

1.2 MB

3.5 inches

Double density

720 KB

3.5 inches

High density

1.44 MB

Formatting of n
ew disk is done to create a number of concentric circles called tracks
on the disk. Tracks are numbered from outside to inside. Each track is again sliced
into smaller parts called sectors.

Remember we usually get pre
formatted disks now a days.

e formatting specifications for various disks:




Sectors per

Bytes per




3.5 inches








3.5 inches








5.25 inches








5.25 inches








Remember the 1.44 MB high
density floppy disks uses two sides to store the
data, has 80 tracks per side and 18 sectors per track. Each sector stores 512 bytes of
data. So, the total number of bytes it can store are:

0*18*512)=1,474,560 bytes, that is 1.44 MB approximately.

In one floppy disk we can store 1,21,400 words. In floppy disk it has tracks and
sectors. In one disk 70 tracks and one track 26 sectors. In one track we can store
3,00,000 to 5,00,000 characters
.In one sector we can store 64 words.


Inspite of emerging technology for different storage media, the hard
disk is still indispensable. It consists of a stack of multiple metal platters coated with
iron oxide and joined by spindle. The ha
rd disk, a set of read/write heads and a
motor to rotate the disks, are sealed in a vacuum chamber to protect it from the dust
and environmental effects.

The rigidity of the hard disk, the multiple platters used and high speed of
revolution allows lots

of data to be stored on the disk and fast access to the data is
made possible. As hard disks are a stack of platters, the term cylinder refers to the
same track across all the disks. Outer most tracks is 0, so the outer most cylinder is
also 0. A compu
ter may have multiple hard disks.

The principle of operation of hard disc is the same as that of floppy disc. Floppy
disc is removable whereas the hard disc used in personal computers are sealed in their

The operation of hard disc and supervising

the control program is called
operating system. It is interference between hardware and software. In operating
system enter the files name and track address allotted to it. When a track is over a
new tack is allotted and the address of that track is also
entered in the table called
FAT [File allocation table].



Compact Disk [Read Only Memory] reads and writes data with the help
of laser beam, which is directed, with the help of lenses, prism and mirrors. The
laser beam
in the form of Lands and Pits stores data. Land is the metal surface
which reflects the light [interpreted as 1] into the sensor and the Pit is the hollow
surface, which scatters the light [interpreted as 0] while data is being read from the
disk. Since
you can write data on it only once, the data, which is tremendous in
volume and does not require changes like videos, multimedia encyclopedias,
multimedia educational software etc. can ideally be stored on it. These days you can
get CD ROM drives with spe
ed varying from quad to 52 X. This speed measures the
rate of data transfer from CD to computer.


You need a CD
Writer [a special pressing equipment] to write on a CD
R. It
does not have physical Pits and Lands, but has a photosensitive dye, wh
ich on heating
changes its composition and emulates the Pits and Lands of a regular CD
Thus, CD
R which is created can be used in a standard CD
ROM drive. The
writing of data on a CD
R is again an irreversible process but most of the CD
Writers al
low you to append the data in the unused space in the subsequent sessions
till the disk is full. A CD
R can store upto generally 74 minutes of video or audio
data in it and has a capacity of 650 MB.


In a CD
RW, it is possible to write many times

on the disk to overwrite the
previously recorded data. A CD
RW is created in the same way as a CD
R but with
the help of CD
Rewriters. A CD
Rewriter can also write on a CD
R but a CD
cannot write on a CD


A DVD or Digital Versatile D
isk is a high
density medium, capable of storing a
length movie on a single disk. A DVD looks like a CD
ROM and DVD players can
also play the CD
ROMs. DVDs will be boon for those applications, which need several
CDs for the storage [like telephone a
ddress data based, encyclopedias, movies etc.] the
capacity of the DVD ranges from 4.7 GB to 17 GB, while that of other forms of CD is just
650 MB. A DVD drive uses a shorter wavelength of light to read the smaller data Pits on
spiral tracks whose turns a
re closer than that of a CD
ROM. This is why so much data
can be packed into a DVD.


As you know that computer interprets everything in zero and one i.e. in binary language.
Each zero and one is called a bit. One byte consists of 8bit
s and stores one character. To make
you understand the units of memory, we are giving the following table.

8 bits


1 byte

1024 Bytes


1 Kilobyte [KB]

1024 kilobytes


1 Megabyte [MB]

1024 megabytes


1 gigabyte [GB]

1024 gigabytes


1 terabyt
e [TB]

A computer has become an essential part of the modern life. It has influenced almost
every aspect of our society. Today computers do much more than to simply compute.
For example, super market scanners help to calculate our grocery bill and also

the inventory, a computerised telephone exchange handles millions of calls and keeps
lines of communications untangled, in banking, automatic teller machines [ATM] let us
conduct banking transactions from virtually any where in the World. But wh
ere did all
this technology come from? To fully understand and appreciate the impact computers
have had on our li
fe, it is of utmost importance

to first understand the architecture and
working of the computer.


A computer system consists

of a number of different components, which work together to make
the system perform an assigned task by accepting the Input and working on it in accordance with
the given instructions to produce the Output.

The computer systems can vary in size, cost and

speed and are used accordingly in suitable types
of work. A computer system consists of three essential components: Keyboard, System Unit and


The Keyboard is used to input the instructions and data into the computer system.

System U

There are a lot of components housed in the system unit. It holds the motherboard, on which the
various component like the memory and the central processing unit (CPU) are fixed. Infact, CPU
is the major component, which executes all the instructions
, does the calculations and takes all the
decisions. System unit also contains power supply unit, to supply power to various components
inside it along with a floppy drive, a CD drive and the hard disk.


A monitor allows the computer to disp
lay the results to the user in the form of text or
graphics. Monitors come in a variety of sizes like 14inches, 15inches, 17inches and 21inches




A language is a medium to communicate with each other. We use com
ponents [symbols,
words and so on] of a language according to the certain rules defined by the language. It is called
the syntax of the language. Each language has its own rules and syntax. Similarly a computer
language, which is needed to interact with

computer, has its own set up rules and syntaxes. While
making programs it is essential to follow these syntax otherwise computer will not be able to
understand anything.

The Computer Language:

Computer languages can be classified in the following th
ree categories based on
complexity of the language.

1. Machine Language

2. Assembly Language

3. High Level Language

1. Machine Language:

As you know all instructions/data that are fed to the computer are converted into a sequence of
bits [0 and 1] as a
computer understands only the binary numbers, which consists of only 2 digits
[0 and 1]. As clear from the name, machine language is directly accepted and executed by the

Note: Machine language is the elementary language of a computer, which co
nsists of binary digits
[0 and 1] only. It is directly executable by the computer and no further translation is required.

It consists of OP CODE [Operation Code], which tells about the function which
computer has to perform, and OPERAND which tells the c
omputer where to store and find the

Limitations of the Machine Languages:

Machine Dependent:

Since internal designs of different types of computer are different. If you
want to execute a machine language program written for one type of computer
or another type of
computer. You need to rewrite the program. So, if you want portability for your program,
machine language is a bad choice.

Difficult to write:

To write program in machine language, a programmer must be completely
familiar with the
architecture of the computer for which he is writing the program. Also giving
every instruction as string of ‘0’ and ‘1’ is not an easy job.

Difficult to modify:

It is also very difficult to find the error in the program or modify it according
to the

new needs.

Advantages of machine language:

Since a machine language program is already in the form of ‘0’ and ‘1’, it is directly
executable by the computer. So execution of the program is very fast. Machine language is
considered to be the first ge
neration language.

2. Assembly Language:

In assembly language, binary operation codes were replaced by the Mnemonics.
Mnemonics are like two or three letter abbreviations. For example, in machine language, if the
operation code for “add,” is “0010”
; its equivalent in assembly language is ‘ADD’. An assembler
is used to further translate it into the machine code so that it can be executed by the computer.

Since mnemonics are abbreviations or symbols, they need to be translated into machine

to get executed. The translator, which does this job in assembly language, is called an
assembler. Assembly languages is considered to be second
generation language. Machine and
assembly languages are also called low level language as they are linked w
ith the hardware. Since
assembly language differs from the machine language in the way of mnemonics mainly, most of the
shortcomings of machine language like machine dependence, difficulty in writing and debugging
the programs etc., are applicable to the
assembly language.

3. High Level Languages:

Machine language and assembly language were used because initially computers came
with very small memory and limited resources. Thus program efficiency could be achieved only
by using hardware
oriented la
nguages. As speed, power and capacity of computer increased, a
need was felt to develop the programs which can make use of this wonderful machine in many
other fields and can be developed by people who are not experts in computer architecture and
. So high level languages came into existence.

level languages (HLL) are the languages with simple English like syntax, which is
easy to understand Basic, Fortran, Pascal, Cobol, C, and C++ are a few such languages. We need
compilers or interprete
rs to change the HLL code to machine code so that it could be understood
and executed by the computer. High
level languages are considered to be third generation

(1) BASIC:

BASIC stands for Beginner's All
purpose Symbolic Instruction Code. I
t is a
comparatively easy language for beginners in the sense that it uses phraseology akin to conventional
ENGLISH. BASIC is the most commonly used language on microcomputers. lt was designed by two
American professors JG Kemeny and Thomas Curtz of Dartmo
uth College USA in 1964.

Many different versions of BASIC are in use. First one is a so
called standard BASIC, but this is so
elementary that nobody uses it. Most microcomputers use a BASIC devised by a company called

Because of its simpli
city, BASIC was used in the first PC to gaip commercial success. It's now by far
the most popular high
level language used in PC systems. This fact makes it one of the most widely
installed computer languages in the world. Interpreters are frequently used
in PC systems to translate
BASIC instructions into machine language code But BASIC language compilers are also available for
these systems. Recreational and educational programs are published in many PC magazines, and these
programs are usually documented


Fortran stands for FORMULA TRANSLATION. It was the first computer language
developed by IBM in 1957. It has been modified since then many times and these versions were given
the names like FORTRAN II. FORTRAN
IV is the most popul
ar version, which was developed in
1966. Latest addition to this is FORTRAN 77, on which even file handling and word processing is
possible. FORTRAN'S syntax is very rigid. It is used in engineering and scientific applications.


Pascal is so
metimes used on small computers and is better structured than BASIC.
PASCAL was designed and developed by Nicolaus Work for teaching computer science.

(4) COBOL:

It stands for Common Business Oriented Language and is the most popular business

today for data processing. It was designed around 1959
60 with a purpose to provide a
common language for business applications.

(5) C:

Its mid level general
purpose language more versatile than BASIC or FORTRAN. It is used
both with Unix and DOS oper
ating systems. The C language was developed at Bell Laboratories in the
early 1970s. It was subsequently used to write the UNIX operating system. Today, AT&T (Bell Labs'
parent) markets a C compiler and UNIX operating system tools as a single software pack
age. There
are many other versions of C that run on pc's and larger machines. (An ANSI standard version is now
available), but its object oriented version C++ is currently becoming the most favored programming

(6) LOGO. It allows even children
to program a microcomputer quickly for drawing pictures etc.

(7) Fourth Generation Languages: These languages are understage of development. Efforts are being
made to see that no elaborate programming is required and languages become user friendly. One s
language SQL was developed by IBM around 1976. SQL is an acronym for "Structured query
language". Commercial relational DBMS packages such as Oracle 7, Ingress 6.4, and Sybase use SQL.

Remember when the input program (called as Source Code) is proces
sed by a language
translator, output is the machine language program called as Object program.

Advantages of High Level Languages:

level languages have lots of advantages over Machine language and Assembly

Hardware Independent:

The p
rograms developed on one type of computer can run or get
executed on other type of computer with no change or little change. Hence lot of effort was saved.

Easy Programming:

It is really easy to write a program in a high level language. The

is more concerned about logic and program development without worrying about the
hardware aspect.


Language translators are software, which are necessary as
every programming language (except machine language) needs to be converted

into the binary
form so that it can be accepted and executed by the computer. In addition these also check and
identify the few errors, which may be present in the program being translated. The three types of
language translators are,

(1) Assembler

) Interpreter

(3) Compiler

1. Assemblers:

To change the program written in Assembly language into the equivalent
machine language code an Assembler is required. It changes the whole program into machine
code so that it can be executed by the compute

2. Interpreters:

Interpreter is used to convert a high level language program code into the
machine language code for execution by converting one statement at a time. Each statement is
translated into machine language and immediately executed. This

way the whole program gets
translated and executed statement by statement.

3. Compilers:

Compiler is used to convert the high
level language program code into the machine
language code for execution. A compiler look at the whole program (instead of lo
oking at it
wise as an Interpreter does) and prepares the equivalent machine code, for the
execution. It takes more time to compile a program but once compiled, a compiled machine code
runs faster than the interpreted program. During the compil
ation process, each coded instruction
is also checked for the satisfactory rules and syntax of the programming language. In case of
errors, the error message is reported to the user.


* * *


As you know a com
puter is a dumb machine, which is completely dependent on you to
give it step
wise instruction and make it work. You need to give instruction to it in the form of
computer program. A set of such program is called Software. Computer software is the
ligence of the computer, which makes it work according to the instructions given in the form
of software.


Software can be classified in following categories depending upon the usage to which it is


System Software


cation Software



System software:

This type of software works at the internal level of computer and tells computer
how to manage its resources. An operating system, which you use and is responsible for providing
an interface between user and c
omputer, is also a type of the System software.

Remember: Operating systems, Assembler, Compiler or Interpreter are also types of the System

Application software:

The software, which makes the computer useful for the people so, that
people ca
n use them for different purposes are called the Application software. These help the
user to work more efficiently, faster and more productively. We can further classify the
application software as follows:


General purpose application software


Custom m
ade application software

General purpose application software (packages): There are general purpose
application software’s like Word processing software, Spread sheets, Database management
software, Desk Top Publishing software etc. avail
able for different needs. For example, by using
MS ACCESS (a database management software), you can develop stock management software for
a company. This software also provides the environment to develop the custom made software.
Let us discuss some of
the commonly used Application software.

(1). Word processing:

Word processing software helps you to create any type of text
document like personal letters, memos and question papers etc. It gives you facilities like spelling
and grammar check, in
sert graphics, merge address list with the letter using the mail merge
feature to generate a letter to each address automatically. You can also format your documents in
attractive styles by applying different font types, sizes, styles, and colours etc. W
ordStar, Word
Perfect and MS Word are some commonly used Word Processing software.

(2). Spread sheets:

A spreadsheet is made up of intersection of rows and columns to form
cells where you can enter numbers, text, formulae and conditions to calcul
ate the result which can
also be viewed graphically in the form of graphs. Any change in the value of any cell will
automatically reflect the changes in the result. Lotus 1
3, Quattropro, MS Excel etc of the some
examples are Spreadsheet software.

(3). Database Management: If you have large data which need to be stored in some organised
manner so that any type of information can be retrieved from it in the form of query and report,
then you need to use some data management software. For example
, If student data of the whole
school can be stored in a database and then reports can be taken out for list of students class
admission number
wise… or in any other way. MS Access, Oracle and FoxPro are some common
examples of Database Management S
ystems software.

(4). Desk Top Publishing: DTP software has gained a lot of popularity in the last few years
because of their magnificent layout and graphical features. Using DTP software’s you can create
documents, which have complex layout, graph
ics and special effects, all sitting on your computer.
The magazines, advertisements, which you read, are made possible only with the help of such
software. Quark press and PageMaker are the commonly used DTP software.

Custom made application software:
Custom made software is the programs developed as per
individual needs. Like Accounting, Library management, fees collection, hotel management etc.
These are developed using the suitable computer language or package.


Utility pro
grams perform the routine but necessary jobs in a computer system. These
programs make life easier for a user by doing several routine and important jobs quickly and in an
easy manner. These jobs include,

(1) Backup of data.

(2) Testing the disk integri

(3) Recovering the accidentally deleted data.

(4) Tracing the operations and steps of program.

Disk Defragmenter, Scandisk are the common utilities provided with Windows software and disk
is utility provided with MS DOS for making disk partitions.

These utilities keep your computer system up to date and allow it to work on its optimum capacity.


1. Fill in the blanks:


Machine and Assembly languages are also called. Level languages.


… Language consists of 0 and 1 only.


level language is ha


In Assembly language ………… are used.


Assembly language needs an. to change it into machine code.

A. Changes the whole program into executable code in one go.


An. Changes program statement
wise into the executable code.


Assembler and Compiler are
the examples of. Software.


Word processor, spreadsheets etc. are ………… software.

MS ACCESS is a type of. Software.


A. is made up of the intersection of rows and columns.


2. Write (T) for True and (F) for False.


level language consists of 0 and 1


A machine language program doesn’t need to be converted further to get executed.


An Assembler is needed for the assembly language program.


A Compiler changes the program statement
wise into the object code.


Operating system is system software.


y program help to do routine jobs in a computer.


MS Word is system software.


Custom made software is developed as the needs of the user.


Operating system is an example of the system software.


You can design advertisements using the DTP software.


3. Very

short type questions.


What is a language?


How can computer language be classified?


Why is machine language directly executable by the computer?


Why are Machine and Assembly language called low
level language?


Name any four High
level languages.


Which lang
uage translators can be used to change High
level language into Machine
language code?


What is a Source code?


What is an object code?


How can you classify Software?


4. Short type questions.


What do you mean by the Syntax of a language?


Why is it diffi
cult to write programs in a machine language?


What are Mnemonics?


What do you mean by “Hardware Independent Language”?


What is an Assembler?


What is an Interpreter?


What is a compiler?


What is System software?


What is Application Software?


What area Utilit

Q. 5. Long type questions.


Explain Application software and their types.


What are the advantages and disadvantages of Machine language?


Write a note on high
level languages.


Write a note on Assembly language.

How a Compiler differs fro
m an Interpreter?




1. Key board

2. CPU

3. Monitor

1. Keyboard helps us to type alphabet, numbers and signs.

2. CPU calculates and compares the work done. It is called the brain of the computer.

3. Monitor finally gives

the result of the comparisons and calculations, which are displayed on its

A computer has many parts. Some of the parts are essential without which the computer will not
work. These parts are called Basic Components.

Some of the parts are n
ot essential but are useful to make the work more easy and interesting.
These parts are called optional components.

Basic Components:

1. The system unit

2. The Monitor

3. The Keyboard

4. The Floppy disk drive

5. The Hard disk drive

Optional Compo

1. Mouse

2. Printer

3. Scanner

4. Multimedia kit

The system unit or CPU:

It controls and does all the computer's main operations. It checks whether all
the parts are connected properly and are working properly. The hard disk drive, floppy
sk drive is usually inside the CPU. All the calculations, storing of data are done by the

Front side of the CPU:

1. Floppy Disk Drive:

There are two types of Floppy disk drives. 5 and one fourth inches floppy disk drive and 3 and
half inches flo
ppy drive. In these drives, we can insert a floppy or take out the inserted floppy.
Through these drives we can read or write data into the system.

2. Floppy Disk Drive Indicators:

There are indicators or lights near the floppy disk drive. They are u
sed to show
whether the drive has a floppy in it or not. If the light is on then the drive has a floppy in
it. Otherwise it has no floppy in it.

3. Power Button:

This is used to switch on or switch off the computer.

4. Reset Button:

This is used to

restart the computer when it is not working properly.

Back of the System Unit:

1. Power sockets:

Power IN Socket is used to plug in the cable (wire) from the electrical board and power out socket
is used to plug in the cable from the CPU to the monitor.

2. Video/Monitor Port:

A cable from the monitor should be plugged here. It is used to transfer data to the monitor that is
to be displayed on the monitor.

3. Parallel Port:

A cable to connect the computer to the printer.

4. Keyboard Port:

A cable to

connect the computer to the keyboard.

5. Serial Ports:

Cable to connect the computer to mouse or modem.

6. Fan Housing:

A fan placed to remove the heat generated from the parts.

7. Compartments for Expansion Cards:

To provide other attachments these
cards are used.

Inside the CPU:

The brain of the computer lies inside the CPU. Its main components are,

1. Mother Board:

All the electronic parts are connected on a board called the Mother Board or
Printed Circuit Board (PCB).

2. Central Processing Un

This is the most important part of the computer. This part takes all the
information and instructions from us and work on it to give us the required results.

3. Math Co

It helps the CPU to do mathematical calculations.

4. RAM:

These parts

are used to store the data temporarily while the computer is
working. But when the computer is switched off the data stored in Ram are lost if we
have not saved the matter by pressing control S. Before saving the matter it is stored in
RAM. RAM means R
andom Access Memory.

5. ROM:

It means Read Only Memory. It tells the CPU what to do when the computer is on. Even the
computer is switched off the data is always available.

6. Hard Disk Drive:

This is the computer's main storage unit. It contains a la
rge amount of data
and programs, which are never destroyed unless the hard disk is damaged. After saving
the file, it will go to the hard disk drive.

7. Disk Drive Control Card:

This is used to take information from the Floppy or to give information to


8. Displays or Printer Adapting Card:

All the information that the computer displays is stored here. It is a link
between the computer, monitor and printer.

9. Power Supply Box:

This changes the high voltage and supplies electricity to all t
he parts of the

10. Speakers:

These help the computer to give out sound.

The Input Devices


We can give instruction to the computer through keyboard. It has got different types of buttons
and switches called keys. The keys are of fi
ve types.

1. Typewriter Keys

some of the typewriter keys are, shift and. is the sign of greater than, shift
and, is less than sign. Slash key or the oblique key is the right side of the. Key. It is used as the per
or by sign. When it is pressed with s
hift key, it will become question mark. Shift and semi colon
will become colon. In the right side of it is apostrophe key. Shift and apostrophe will be inches
symbol or inverted comma sign. Left and right brackets are near p and 9 and 0 with the shift
are also left and right brackets. Shift and left bracket near p will become another type of bracket,
which is called left grace, and shift and right bracket will become right grace. Near 0 is dash and
then the equals key. In the right side of the =
key there is the back slash key. Shift and dash at a
time will underline the whole line if we go on pressing dash without leaving the shift key. If we
press the dash key holding the shift key for 4 to 5 times and press enter without pressing any other
y, then also the whole line will be underlined. If we press space bar, then the underline will stop
there. Shift and equals at a time is the sign of plus. Shift and back slash key will become vertical
bar. Shift key and 8 will be the sign of star. Shi
ft and 7 is the sign of small and. Shift and 5 is the
sign of percentage. Shift and 4 is the sign of dollar and shift and 3 is the sign of number. Shift and
1 is the sign of exclamatory. Shift and 2 is the sign of at the rate of. Shift and 6 is the si
gn of
carrot. In MS Word to type the mathematical signs or symbols, we have to go to the symbols
submenu and press enter on it. It is in the insert menu.

2. Function Keys

There are 12 function keys.

3. Cursor Control Keys

such as Left arrow, Rig
ht arrow, Up arrow, Down arrow key, page up,
page down key, home key and end key.

4. Numeric Keypad

5. Special keys

such as, escape key, tab key, caps lock key, shift keys, control keys, alt keys, enter
key, back space key, insert key, delete key, print

screen key, pause key and scroll lock key.

Print screen helps to print the matter, at present displayed, on the screen.

Pause key helps to stop the matter running down the screen.

Scroll lock key locks the facility of scrolling the matter on the screen.

Insert key helps to insert a character at the present place of the cursor.

LED status indicators such as num lock indicator, caps lock indicator and scroll lock indicator
show whether the keys are switched off or switched On.


It is a rectangular b
ox with a ball inside it. The mouse cursor, which looks like an arrow mark can
move in all directions unlike the keyboard cursor. It is highly used on Windows based programs.
The keyboard cursor can move only in straight lines but the mouse cursor can m
ove in all
directions. On the top left corner and right corner of the mouse there are two buttons. The left
button is similar to the enter / Return key of the keyboard. The right button helps to display drop
down list in many software’s. At times it is

used to function like an Escape key of the keyboard.
When the mouse cursor changes into an hourglass symbol then it means that computer is working
on our instructions and we should wait until it gets converted into arrow symbol.

The Output Devices



The monitor of the computer is like a television. It is called Visual Display Unit or V D U. On the
screen of the monitor we can see all the information, which we have instructed the computer to
store and display. The monitor is also called
Cathode Ray Tube or CRT. The picture or the
matter that we see on the screen is made up of small dots called pixels. All that we type on the
keyboard will be seen on the monitor.

The cursor is a double line showing the current position on the screen.
If a letter is typed it will be
seen under the cursor and the cursor will move to the next position.

The monitors can be black and white monitors or colour monitors.

The printer:

It is an output device, which gives out the information as printouts on p
apers. The speed of
printers is measured by pages per minutes or characters per second.

The different types of printers are Dot matrix printers, Line printers, Inkjet printers and Laser

Storage Media:

Floppy disks and hard disks are the two

types of storage media. They are used to store data
permanently even when the computer is shut down.

Floppy Disk:

Floppy disks are used to store data and also to transfer data from one computer to another. The
features of floppy disk are:

1. Label Ar

Here we have to affix label or sticker and name the contents of the floppy.

2. Read / write openings:

This is the area where the read / write heads of the floppy are able to read contents of a floppy or
write contents to a floppy.

3. Write protect

The small write protect switch available on the floppy prevents anyone from intentionally or
accidentally changing or erasing the contents of the floppy. To write protect three and half inches
floppy push the button to keep the whole open.

dware and Software

These are the most important requirements for a computer to work properly.



means the parts of a computer
Such as input devices, output devices,
system unit and storage devices.



means all t
he instructions or programs given to the computer. Without
software the computer will not work. Software is classified into two parts.


System Software.

B. Application Software.

MS Word is the application software. Without system software like MS Off
MS Word or the application software cannot function. The operating systems like
windows 98 are also called system software because without an operating system no
application can function.




Escape key:

It means to re
move any type of dialogue boxes, message boxes etc.



Tab is used to give 5 spaces directly.


One tab = 5 spaces.

B. Tab is used to move one option to next option.

C. Tab is used to come to previous option with using Shift and Tab key.

D. Tab is als
o used to move one page to another page in the dialogue boxes with using
Control and Tab.

E. Tab is used move between the application or documents or files with the using ALT
and TAB.

F. Tab is used to move from one cell to next cell.


It is u
sed to change the small letters into the capital letters

Shift used to enter the symbols in the documents

Shift used for selecting the letters with the help of other keys


a. Control

is used to stop the JAWS speech and to stop the cursor.

b. Control key is used to link with other keys to make commands at the time of working with
different applications.


a. It is used
to open the menu box and to navigate between the main menus and sub menus.

b. Alt
to link with other ke
ys as commands.

c. ALT is used to toggle between the applications with TAB key.


After activating the application button some menus will take place. Particularly we use 3
and half floppy option to sent files and folders into flop
py and we can use other menus for
different purposes.



Activate the menu.

b. At the time of changing the line.

c. At the time of deleting files and folders with the link to delete key.

d. To give extra space between the lines.


Left arrow is used to go to the previous character.

Down Arrow is used to go to next line.

Up Arrow is used to go to previous line.

Right Arrow is used to know the next character.


a. Insert is used to know the time with the link of F12 k

b. It is used to
link with
other keys

as commands like Insert f12 to know the time, Insert
F to know the details of the text format, Insert V, Insert F4 and Insert F1 etc.

c. Insert Escape is used to refresh the screen.


a. It is used de
lete the text in the document.

B. It is used to delete the blank columns

C. It is also used with other keys.


It is used to bring the cursor to the starting point.

B. It is also used to as a command with other keys.



It is used

to take the cursor to the last character of the line.

b. End Key is used as a command with other keys.


a. Page up and page down keys are used to go to one page to next page or to go to
previous page with link to the Control Key.

b. Alt Page Up and Alt Page Down

are used to move from one screen to another screen

excel application.




Jaws MEANS Job Access With Speech.

Jaws is screen reading software which it reads not only contents on the desk top but also
the text

matter in all types of applications as well as internet and other programming
languages. .

To open the Jaws press “Left window key, then press P [programmes] and then press J
and J or go to run dialogue box by pressing LEFT WINDOW BUTTON and then press

Then type the JFW and press ENTER KEY. Then “JAWS” for windows are ready to
run the system.

To close the Jaws press “Insert F4 and give Enter key.