The document provides an overview of computers including: 1. Definitions of a computer as a programmable machine that processes data according to instructions. 2. The evolution of computers from early mechanical calculating devices to modern electronic digital computers. 3. Classifications of computers based on factors like size, purpose, and data type. 4. Descriptions of the components and organization of a basic computer system including input, processing, output, and storage units. 5. Various uses of computers in fields like education, business, science, recreation and more.

1. Index
• Computer
• Evolution of computer
• Computer generations
• Characteristics of computer
• Uses of computer
• Classification of computer
• Computer organization

2. Computer
The word “computer” comes from the word “compute”, which means, “to calculate”. Hence,
people usually consider a computer to be a calculating device that can perform arithmetic
operations at high speed.
A computer is a programmable machine designed to perform arithmetic and logical operations
automatically and sequentially on the input given by the user and gives the desired output after
processing. However, more than 80% of work done by computers today is of non-mathematical
or non-numerical nature.
More accurately, we can define a computer as a device that operates upon data. Data can be
anything. It comes in various shapes and sizes depending upon the type of computer application.
A computer can store, process and retrieve data as and when required. The fact that the
computer processes data is so fundamental that many people have started calling it a data
processor.
There are various ways in which computer can be defined but on the basis of its power the most
generalized and popular definition is -
“A computer is an electronic device which processes or manipulates the data strictly according
to the instructions given and produces meaningful result efficiently, effectively and reliably.”
“Computer can be defined as any machine, which can accept data, in prescribed form, process
the data and supply the result of processing in a specified format as information or as signals to
control automatically some further machine or process.”
- Dictionary of Computers – Penguin

3. Evolution of computers
Like civilizations, computers have also evolved over a period of time. Some of the important
stages of computer evolution are listed below:
 Abacus is considered the earliest calculating device invented around 600 B.C., it is a rack of
beads used to add or subtract by positioning the beads correctly.
 In 1642, Blaise Pascal invented first mechanical adding machine. The innovation and
invention continued according to the needs of people.
 In 1822, a Professor of Cambridge University, Charles Babbage Known as father of
computer, invented “Difference Engine” which can produce reliable tables, as at that time
mathematical and statistical tables were prepared by the clerks which consumed lot of
precious time and was also very much prone to errors.
 In 1942, he designed new machine “Analytical Engine” which was planned to be fully
automatic and capable of performing all basic arithmetic calculations. Somehow this
machine was not produced. But his idea gave most basic fundamentals of computer design.
 In 1937, Haward Aiken of Harvard University, in collaboration with IBM developed “Mark
I” the punch card operated machine which could perform all the arithmetic calculations.
 In 1943, ENIAC (Electronic Numerical Integrator and Calculator) was developed by a
design team headed by Professor Prosper Eckert and John Mauchly of Moore College of
Engineering, University of Pennsylvania. ENIAC was very complex to be programmed but
it was capable of performing calculations more than 200 times of Mark I.
 In 1946, Professor Jon Von Neumann developed EDAVC (Electronic Discrete Variable
Automatic Computer). This computer stored the data and instructions in sequence, in
memory in the binary form (0 & 1). For this reason, modern computers are known as digital
computers.

4.  UNIVAC (Universal Automatic Computer) was first digital computer installed in Census
Bureau in 1951. By this time evolution was carried out at different places, but IBM
(International Business Machine) came out first and produced machines for business.
Computer Generations
Generation Years Switching Storage Switching MTBF Software Application
Device Device Time
First 1949- Vacuum Tubes Acoustic delay 0.1 – 1 30 Machine Mostly scientific.
1955 lines, mille minutes and Later simple
magnetic second to 1 Hr assembly business systems.
drum. 1 languages.
Kbytes Simple
memory monitors.
Second 1956- Transistors Magnetic core 1 – 10 About High level Extensive business
1965 main memory, micro 10 Hrs languages, applications.
tapes and disk second FORTRAN, Engineering design
peripheral COBOL, optimization
memory. 100 Algol, scientific research.
Kb main Batch
memory. Operating
System
Third 1966- Integrated High speed 0.1 – 1 About FORTRAN Database
1975 Circuits(IC) magnetic micro 100 Hrs 4, COBOL management
cores. Large second 68, PL/I system. Online
disks (100 Timeshared systems.
MB) 1MB Operating
main memory. System
Fourth- I 1975- Large Scale Semiconducto 10 – 100 About FORTRAN Personal
Phase 1984 Integrated r memory. nano 1000 &&, Pascal, computers.
Circuits Winches disk. second Hrs ADA, Distributed
Microprocessors 10 MB main COBOL 74, systems. Integrated
memory. Concurrent CAD/CAM real

5. 1000MB Pascal time control.
disks. Graphic oriented
system.
Fourth – II 1985- Very Large Semiconducto 1 – 10 About C, C++. Simulation
Phase Present Scale Integrated r memory. 1 nano 10000 JAVA, visualization,
Circuits. Over 3 GB main second Hrs PROLOG, Parallel computing,
million memory. 100 FP Virtual reality,
transistor per GB disk. Multimedia.
chip
*MTBF - Mean time between failures of processor.

6. Characteristics of Computer
Speed
Computers work at an incredible speed. A powerful computer is capable of performing about 3-
4 million simple instructions per second.
Accuracy

7. In addition to being fast, computers are also accurate. Errors that may occur can almost always
be attributed to human error (inaccurate data, poorly designed system or faulty instructions /
programs written by the programmer)
Diligence
Unlike human beings, computers are highly consistent. They do not suffer from human traits of
boredom and tiredness resulting in lack of concentration. Computers, therefore, are better than
human beings in performing voluminous and repetitive jobs.
Versatility
It means the capacity to perform completely different type of work. You may use your computer
to prepare payroll slips. Next moment you may use it for inventory management or to prepare
electric bills.
Storage
The Computer has an in-built memory where it can store a large amount of data. You can also
store data in secondary storage devices such as pen drive, DVD, CD, etc. which can be kept
outside your computer and can be carried to other computers.
No IQ
Computer is a dumb machine and it cannot do any work without instruction from the user. It
performs the instructions at tremendous speed and with accuracy. It is you to decide what you
want to do and in what sequence. So a computer cannot take its own decision as you can.
No Feeling
It does not have feelings or emotion, taste, knowledge and experience. Thus it does not get tired
even after long hours of work. It does not distinguish between users.
Uses of Computer
Education:
Getting the right kind of information is a major challenge as is getting information to make
sense. College students spend an average of 5-6 hours a week on the internet. Research shows

8. that computers can significantly enhance performance in learning. Students exposed to the
internet say they think the web has helped them improve the quality of their academic research
and of their written work. One revolution in education is the advent of distance learning. This
offers a variety of internet and video-based online courses.
Health and Medicine:
Computer technology is radically changing the tools of medicine. All medical information can
now be digitized. Software is now able to computer the risk of a disease. Mental health
researchers are using computers to screen troubled teenagers in need of psychotherapy. A
patient paralyzed by a stroke has received an implant that allows communication between his
brain and a computer; as a result, he can move a cursor across a screen by brainpower and
convey simple messages.
Science:
Scientists have long been users of computer. A new adventure among scientists is the idea of a
“collaboration”, an internet based collaborative laboratory, in which researchers all over the
world can work easily together even at a distance. An example is space physics where space
physicists are allowed to band together to measure the earth’s ionosphere from instruments on
four parts of the world.
Business:
Business clearly sees the interest as a way to enhance productivity and competitiveness. Some
areas of business that are undergoing rapid changes are sales and marketing, retailing, banking,
stock trading, etc. Sales representatives not only need to be better educated and more
knowledgeable about their customer’s businesses, but also must be comfortable with computer
technology. The internet has become a popular marketing tool. The world of cybercash has
come to banking – not only smart cards but internet banking, electronic deposit, bill paying,
online stock and bond trading, etc.
Recreation and Entertainment:
Our entertainment and pleasure-time have also been affected by computerization. For example:

9. i) In movies, computer generated graphics give freedom to designers so that special effects and
even imaginary characters can play a part in making movies, videos, and commercials.
ii) In sports, computers compile statistics, sell tickets, create training programs and diets for
athletes, and suggest game plan strategies based on the competitor’s past performance.
iii) In restaurants, almost every one has eaten food where the clerk enters an order by indicating
choices on a rather unusual looking cash register; the device directly enters the actual data into a
computer, and calculates the cost and then prints a receipt.
Government:
Various departments of the Government use computer for their planning, control and law
enforcement activities. To name a few – Traffic, Tourism, Information & Broadcasting,
Education, Aviation and many others.
Defense:
There are many uses computers in Defense such as:
1) Controlling UAV or unmanned air-crafts an example is Predator. If you have cable I would
recommend watching the shows “Future Weapons" and “Modern Marvels". The show future
weapon gives an entire hour to the predator.
2) They are also used on Intercontinental Ballistic Missiles (ICBMs) that uses GPS and
Computers to help the missile get to the target.
3) Computers are used to track incoming missiles and help slew weapons systems onto the
incoming target to destroy them.
4) Computers are used in helping the military find out where all their assets are (Situational
Awareness) and in Communications/Battle Management Systems.
5) Computers are used in the logistic and ordering functions of getting equipments to and
around the battlefield.

10. 6) Computers are used in tanks and planes and ships to target enemy forces, help run the
platform and more recently to help diagnose any problems with the platforms.
7) Computers help design and test new systems.
Sports:
In today's technologically growing society, computers are being used in nearly every activity.
Recording Information
Official statistics keepers and some scouts use computers to record statistics, take notes and chat
online while attending and working at a sports event.
Analyzing Movements
The best athletes pay close attention to detail. Computers can slow recorded video and allow
people to study their specific movements to try to improve their tendencies and repair poor
habits.
Writers
Many sportswriters attend several sporting events a week, and they take their computers with
them to write during the game or shortly after while their thoughts are fresh in their mind.
Scoreboard
While some scoreboards are manually updated, most professional sports venues have very
modern scoreboards that are programmed to update statistics and information immediately after
the information is entered into the computer.
Safety and Security
Computers have aided in the design of safety equipment in sports such as football helmets to
shoes to mouth guards. Computer becomes an integral part for security. Many security systems
have been developed and used through computers.

11. Classification of Computer

12. On the basis of Type of Data

13. • Analog Computers
Analog Computer is a computing device that works on continuous range of values. The results
given by the analog computers will only be approximate since they deal with quantities that
vary continuously. It generally deals with physical variables such as voltage, pressure,
temperature, speed, etc.
• Digital Computer
A computer that performs calculations and logical operations with quantities represented as
digits, usually in the binary number system i.e. 1 and 0.
• Hybrid Computer (Analog + Digital)
A combination of computers those are capable of inputting and outputting in both digital and
analog signals. A hybrid computer system setup offers a cost effective method of performing
complex simulations.
On the basis of Purpose
• General Purpose Computers
The general purpose computers are designed to solve a large variety of applications through the
use of stored program/instructions in its internal storage. However, this versatility is achieved at
the expense of speed and efficiency of the computer. Most digital computers are general
purpose computers.
• Special Purpose Computers
These are built to solve a specific problem. In these machines, the computer program for
solving the problem is built right into the computer. Their operations are specific and are
usually made for a single customer. Some examples are: automatic teller machine (ATM) for 24
hours banking, industrial process system, etc.
On the basis of Size and Capacity
• Super Computers

14. Large scientific and research laboratories as well as the government organizations have extra
ordinary demand for processing data which required tremendous processing speed, memory and
other services which may not be provided with any other category to meet their needs.
Therefore very large computers used are called Super Computers. These computers are
extremely expensive and the speed is measured in billions of instructions per seconds.
Supercomputers are mainly being used for whether forecasting, biomedical research, remote
sensing, aircraft design and other areas of science and technology. Examples of supercomputers
are CRAY YMP, CRAY2, NEC SX-3, CRAY XMP and PARAM from India.
• Main Frame Computers
The most expensive, largest and the most quickest or speedy computer are called mainframe
computers. These computers are used in large companies, factories, organizations etc. the
mainframe computers are the most expensive computers; they cost more than 20 million rupees.
In these computers 150 users are able to work on one C.P.U. The mainframes are able to
process 1 to 8 bits at a time. They have several hundreds of megabytes of primary storage and
operate at a speed measured in nano second.

15. • Mini Computers
Mini computers are smaller than mainframes, both in size and other facilities such as speed,
storage capacity and other services. They are versatile that they can be fitted where ever they are
needed. Their speeds are rated between one and fifty million instructions per second (MIPS).
They have primary storage in hundred to three hundred megabytes range with direct access
storage device.
• Micro Computers
These are the smallest range of computers. They were introduced in the early 70’s having less

16. storing space and processing speed. Micro computers of today are equivalent to the mini
computers of yesterday in terms of performing and processing. They are also called “computer
of a chip” because its entire circuitry is contained in one tiny chip. The micro computers have a
wide range of applications including uses as portable computer that can be plugged into any
wall. It includes:
Desktop Computer: a personal or micro-mini computer sufficient to fit on a desk.
Laptop Computer: a portable computer complete with an integrated screen and keyboard. It is
generally smaller in size than a desktop computer and larger than a notebook computer.
Palmtop Computer/Digital Diary /Notebook /PDAs: A hand-sized computer. Palmtops have
no keyboard but the screen serves both as an input and output device.

17. Computer Organization
Basic Computer Organization
Input Unit
The first step in any processing activity is providing data and the instructions for processing the
data. Since computer cannot understand human language, therefore this communication has to
be done in a language which computer can understand. The unit that perform this task of
communicating data and instructions to the computer is referred to as Input Unit. This data is in
a coded form (human understandable form), on an input medium and is read and translated by
an input device into a form which is understandable by computer i.e. binary form.

18. Some of the input devices are as follows:
• The Mouse
Mouse is an input device that is used with personal computer. Earlier it rolls on a small ball but
now uses optical technology and has two or three buttons on the top. When you roll the mouse
across a flat surface the screen censors the mouse in the direction of mouse movement. The
cursor moves very fast with mouse giving you more freedom to work in any direction. It is
easier and faster to move through a mouse.
• The Keyboard
This is the standard input device attached to all computers. The layout of keyboard is just like
the traditional typewriter of the type QWERTY. It also contains some extra command keys and
function keys. It contains a total of 101 to 104 keys. You have to press correct combination of
keys to input data. The computer can recognize the electrical signals corresponding to the
correct key combination and processing is done accordingly.
• Tracker Balls

19. Track ball is similar to the upside - down design of the mouse. The user moves the ball directly,
while the device itself remains stationary. The user spins the ball in various directions to effect
the screen movements.
• Scanners
Scanners are used to enter information directly in to the computers memory. This device works
like a Xerox machine. The scanner converts any type of printed or written information including
photographs into digital pulses, which can be manipulated by the computer.
• Touch Pads
A touch pad is a laptop / palmtop device and responds to pressure. Conjunction with a special
pen they can be used by graphic artists wishing to create original, digital artwork.
• Light Pens

20. It is a pen shaped device used to select objects on a display screen. It is quite like the mouse (in
its functionality) but uses a light pen to move the pointer and select any object on the screen by
pointing to the object.
• Joysticks
Many games require a joystick to play the game. Any different types, but it may be worth
investing in a good quality one that is strong to withstand the rough treatment it will get from
the kids while they are playing the games and one that can respond to movement in three axis
directions.
• Microphones
This micro phone is used to convert human speech into electric signals. The signal pattern is
then transmitted to a computer when it’s compared to a dictionary of patterns that have been
previously placed in a storage unit of computer. When a close match is found, the word is
recognized.

21. • Web Cams
Small digital movie camera (a web cam) is mounted on the PC monitor to allow two way
communication involving not just text communication, but sound and video as well.
• Digital Cameras
It converts graphics directly into digital form. It looks like an ordinary camera, but no film is
used therein, instead a CCD (changed coupled Divide) Electronic chip in used. When light falls,
on the chip though the lens, it converts light waves into electrical waves.
• Bar Code Reader
This device reads bar codes and coverts them into electric pulses to be processed by a computer.
A bar code is nothing but data coded in form of light and dark bars.

22. Output Unit
The data and instruction fed into the system through input unit go to memory of the computer.
The data is processed according to the instructions given and result is again stored in memory of
the computer in the form of binary digits 0 and 1. These results have to be communicated to the
outside world in human acceptable form. This function of communicating (through conversion)
the result of processing to the human being for decision making is performed by Output Unit.
Here are some most common output devices given below:
• Visual Display Unit
The most popular input/output device is the Visual Display Unit (VDU). It is also called the
monitor. A Keyboard is used to input data and Monitor is used to display the input data and to
receive massages from the computer. A monitor has its own box which is separated from the
main computer system and is connected to the computer by cable. In some systems it is compact
with the system unit. It can be color or monochrome.
• Printer
It is an important output device which can be used to get a printed copy of the processed text or
result on paper. There are different types of printers that are designed for different types of

23. applications. Depending on their speed and approach of printing, printers are classified as
impact and non-impact printers. Impact printers use the familiar typewriter approach of
hammering a typeface against the paper and inked ribbon. Dot-matrix printers are of this type.
Non-impact printers do not hit or impact a ribbon to print. They use electro-static chemicals and
ink-jet technologies. Laser printers and Ink-jet printers are of this type. This type of printers can
produce color printing and elaborate graphics.
• Plotter
Plotters are used to print graphical output on paper. It interprets computer commands and makes
line drawings on paper using multicolored automated pens. It is capable of producing graphs,
drawings, charts, maps etc.
• Audio Output: Speakers
The Audio output is the ability of the computer to output sound. Two components are needed:
Sound card – Plays contents of digitized recordings, Speakers – Attached to sound card.
• Projector

24. An output device that takes the display of a computer screen and project a large version of it
onto a flat surface. Projectors are often used in meetings and presentations to help make sure
everyone in the room can view the presentation.
Storage Unit
Data and instructions entered into a computer system through input units have to be stored
inside the computer before actual processing starts. Similarly, results produced by the computer
after processing have to be kept somewhere inside the computer system before being passed on
to an output unit. Moreover, a computer must also preserve intermediate results for ongoing
processing. Storage unit of a computer system caters to all these need. It provides space for
storing data and instructions, intermediate results, and the results for output.
Storage unit of all computers is comprised of the following two types of storage:
Primary Storage
Primary storage, also known as main storage or memory, is used to hold pieces of program
instruction and data, intermediate result of processing, and recently produced result of those
jobs on which computer is currently working. These pieces of information are represented
electronically in the main memory chip’s circuitry and while it remains in the main memory,
CPU can access it directly at a very fast speed. It is volatile in nature i.e. as soon as the
computer is switched off or reset, the information hold by it is erased. Primary storage normally
has limited storage capacity and is very expensive. In modern computers it is made up of
semiconductors.
It is of two types:
• Random Access Memory (RAM)

25. Random Access Memory (RAM) is the best known form of computer memory. The Read and
write (R/W) memory of a computer is called RAM. The RAM is a volatile memory; it means
information written to it can be accessed as long as power is on. As soon as the power is off, it
can not be accessed. RAM holds data and processing instructions temporarily until the CPU
needs it. RAM is considered “random access” because you can access any memory cell directly
if you know the row and column that intersect at that cell. RAM is made in electronic chips
made of so called semiconductor material, just like processors and many other types of chips.
• Read Only Memory (ROM)
One major type of memory that is used in PCs is called read - only memory or ROM for short.
ROM is a type of memory that normally can only be read, as opposed to RAM which can be
both read and written. There are two main reasons that read-only memory is used for certain
functions within the PC:
Permanence: The values stored in ROM are always there, whether the power is on or not. A
ROM can be removed from the PC, stored for an indefinite period of time, and then replaced,
and the data it contains will still be there. For this reason, it is called non-volatile storage.
Security: The fact that ROM cannot easily be modified provides a measure of security against
accidental (or malicious) changes to its contents.
Secondary Storage
Secondary Storage of a computer is also known as auxiliary storage, is used to take care of the
limitations of primary storage. That is, it supplements the limited storage capacity and volatile

26. characteristic of primary storage. This is much cheaper than the primary storage and can retain
information even when the computer switches off or resets. Secondary storage holds the
program instructions, data and information of those jobs on which the computer system is not
currently working but needs to hold them for processing later.
The different types of secondary storage devices are currently in use are as follows:
Arithmetic and Logic Unit

27. This unit performs the arithmetic and logical operations on the data and instructions supplied by
the input devices, under the command from the control unit. The basic arithmetic operations
performed are addition, subtraction, multiplication and division, which are built into the control
unit. In addition to arithmetic operations computer can perform logical operations as well e.g.
comparing two or more numbers or letters, making decision according to the defined criteria,
etc. this is a place where data is manipulated and the result are communicated to memory.
Control Unit
This is the most important unit in a computer system. It supervises the entire operation of a
computer system; it acts as a traffic policeman, which controls the traffic of data and electronic
signals between various units and components of computer. It instructs the input device when to
start and stop the input to memory, it transfer the input information from memory to arithmetic
and logic unit, it selects the proper operations to be carried out, it directs the memory unit when
to start and stop the transfer of information to output unit, etc. therefore the function of control
unit in a computer is to maintain order and direct the flow of operations in a proper manner. It
acts like central nervous system for various units of a computer.
Central Processing Unit
Control Unit, Arithmetic Logic Unit of a computer system are together known as Central
Processing Unit (CPU). The CPU is the brain of a computer system. In human body, the brain
takes all major decisions and other part of the body function as directed by the brain. Similarly,
in a computer system, all major calculations and comparisons takes place inside the CPU and
the CPU is responsible for activating and controlling the operations of other units of the
computer system.

28. Bibliography
Books of Reference:
• Sinha P.K., Sinha Priti, “Computer Fundamentals”, BPB Publications, New Delhi, Fourth
Edition ( revised and reprinted), 2010.
• Saini A.K., Kumar Pradeep, “Computer Applications in Management”, Anmol Publications
Pvt. Ltd., New Delhi, 2009.
Websites of Reference:
• http://www. ecomputernotes.com
• http://www.kkhsou.in
• http://en.wikipedia.org
• http://www.google.co.in/imghp?hl=en&tab=wi