What is Computer?
• Computer is an computational device.
• an electronic device designed to accept data, perform prescribed
mathematical and logical operations at high speed, and display the
results of these operations.
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• A computer is a programmable machine designed to automatically carry
out a sequence of arithmetic or logical operations. The particular
sequence of operations can be changed readily, allowing the computer
to solve more than one kind of problem. An important class of computer
operations on some computing platforms is the accepting of input from
human operators and the output of results formatted for human
consumption. The interface between the computer and the human
operator is known as the user interface.
Characteristics of computer
• Speed It refers to the speed of computation. A computer is a high-
speed device. It can perform a task in seconds for which, manual
manpower may require a year or even more. The units of speed
are measured in microseconds and nanoseconds. A computer is
capable of performing 3 to 4 million simple arithmetic calculations
per second.
• Accuracy It refers to the precision with which calculations can be
done. A computer maintains high degree of accuracy provided
there is no human mistake i.e. faulty programming or inaccurate
dates. If 10 million calculations are to be performed, the computer
will do with same accuracy.
• Consistency It means continuous. A computer can work for hours
without lack of concentration or emotional feelings. It does not get
tired and will do the jobs with same speed and accuracy even if is
first job or its millionth job.
• Versatility It means dynamic or varied. A computer can
perform various types of jobs like it can do scientific
calculation, make drawings, etc. It can change over to
various types of jobs within a very short span of time.
With the help of multitasking, the processor can switch to
various jobs
• Malfunction Just like any man -made machine, it is
subject to occasional breakdown or malfunction.
• Wrong output It cannot correct wrong instructions by
itself so; wrong input results in wrong output.
• No feelings since computer is a machine it is free from
• Versatility It means dynamic or varied. A computer can
perform various types of jobs like it can do scientific
calculation, make drawings, etc. It can change over to
various types of jobs within a very short span of time.
With the help of multitasking, the processor can switch to
various jobs
• Malfunction Just like any man -made machine, it is
subject to occasional breakdown or malfunction.
• Wrong output It cannot correct wrong instructions by
itself so; wrong input results in wrong output.
• No feelings since computer is a machine it is free from
Generation of Computers
• The progress of human technology to make life easier has brought
many changes in computers. Generation of computers details, how
computer technology has progressed to its current state from
ancestors. Thus, ‘Generation’ signifies the advancements in
computers. In 600BC a manual device was used for purpose of
calculation.
• First Generation Computers
• Vacuum tube technology was used in this generation of computers.
• ENIAC (Electronic Numerical Integrator & calculator) was first general
purpose computer developed in USA was designed using 1800
vacuum tubes (Diode or Triode valves)
• EDVAC (Electronic Discrete Variable auto Computer) was able to
store programs and data in the memory. It is considered, as first
digital computer using 1’s and 0’s to represent all characters.
• UNIVAC –I (Universal automatic Computer) first digital computer
produced on mass scale for commercial use.
Advantages of First Generation computers
• They were faster than other computing devices
• Electronic devices now were able to do computation,
as this generation had shown the technology
Disadvantages of First Generation computers
• Vacuum tube required lots of power for operation
• Vacuum tube generated a lot of heat, hence air-
conditioning was required
• Computers were bulky and were not portable
• Computers occupied a lot of space
• Due to frequent breakdown, constant maintenance
was required
Second Generation Computers
They were designed using transistors. Ferrite core was
used for main memory. For secondary memory Magnetic
tape/ Disks/Drums were used. High-level languages like
FORTRAN, ALGOL COBOL, were used for programming.
SGC were more reliable and faster. They used to generate
less heat but air-conditioning was required. IBM-1620,
IBM – 7090 CDC-1604, PDP-1, PDP-5.
Advantages of Second Generation computers
• They were faster in computation, than the first generation
computers
• They occupied less space, as transistors were small, as
compared to the first generation computers
Disadvantages of Second Generation computers
• Transistors generated heat, hence air-
conditioning was required
• Computers were still bulky and were not
portable
• Computers occupied a lot of space
• Due to breakdown, frequent maintenance was
required
Third Generation Computers
They were designed using integrated circuits (IC’s)
technology. They have core magnetic memory or
semiconductor memories (RAM and ROM)
Computers were having the cache memory feature.
Secondary storage memories were similar to 2nd
generation computers. Concept of multiprocessing
and multiprogramming was introduced. IC chip
means integrated circuit chip i.e. a chip is an area less
than 5mm. Square and IC chip means integrating or
joining electronic circuits in less 5mm. Square area.
Advantages of Third Generation computers
• They were faster in computation, than the second-
generation computers
• They occupied less space, as IC chip were small, as
compared to the transistors
• Due to high reliability less maintenance was
required
Disadvantages of Third Generation computers
• IC chip technology was more complex and thus,
expert persons were required
Fourth Generation Computer
Its features are
• Uses VLSI chips for memory & CPU
• RAM 1to 256 MB or more available
• Cache memory on CPU chips
• Concept of super computer having more than 1 CPU’s
• Additional Numerical processor
• Larger hard disks 1.2-6.5 GB or more
• Optical Disks for mass storage
• Audio/Video capability
• e.g. IBM PC 8086/8088/80286/80386/80486,
PENTIUM-MMX, PENTIUM II/III, IBM-AS/400, CRAY Y-
Advantages of Fourth Generation computers
• They were faster in computation, than the third
generation computers
• They occupied less space, as it shrunk the area
required by electronic circuits
• They were more reliable and low maintenance was
required
Disadvantages of Fourth Generation computers
• Due to breakdown, frequent maintenance was
required
• IC chip technology was more complex and thus, expert
persons were required
Fifth Generation Computers
The aim of 5th generation is to bring machines with general
intelligence, the ability to reason logically. It is not just data processing
but knowledge processing. Some of the expected features of 5th
generation computers are as follows
• These computers will use ULSI chips (Ultra Large scale integration) to
achieve more efficiency
• The input and output is speech & graphics, in future they will
understand languages like English, Japanese
• Computer will do the job of programming
• Extensive use of parallel processing will be used
• All data may not be stored in main memory; they may flow through
processing units by activating them according to the computers
• These computers are yet to come and scientists are doing research on
them. Computer will be having its own intelligence. Hence, it will take
decisions on its own. ULSI and AI (Artificial Intelligence) technology
will be used in these computers.
• Applications of Computer
Some of the fields where computers are being used are
• Offices
Computers are widely being used in offices to perform day to day works like
preparation of forms, letters contract documents memorandums, project
reports, create budgets, communicate with co-workers, find information
etc. Computers are vital in accounting department, for manipulating large
set of numbers, which accounting departments do daily. Word processing
and spreadsheet packages like work-sheet Ami-pro, Excel, are popular office
packages that help in creating a paper less office.
• Publication and Printing
Popularly known as desktop publishing, design, layout and composition of
books, brochures leaflets, visiting cards, letter heads using popular
packages like PageMaker, Ventura, CorelDraw, QuarkXPress etc. Output of
the designs is taken on laser printer. Using a camera negative/ positive
design is prepared which is used in offset/screen printing according to the
colors specified.
• Education
In educational departments, institutes, computer is used as teaching aid,
which is referred as computer assisted instructions (CAI). The CAI
programs can be prepared in a variety of modes like tutorial, problem
solving modeling etc. For multimedia computers CD’s are also
available for educational /training purposes on almost every subject
with audio/video features known as CBT (Computer Based Training).
• Computer Aided Designing
Computer Aided Design (CAD) and computer aided manufacturing (CAM)
are one of the most powerful application applications Engineers,
scientist and designers use CAD software to design a machine, car,
building etc. These designs can be viewed in 3D before the
production of machines. Computers can also control manufacturing
machines like drill, lathe machines. An integrated CAD/CAM system
help to produce quality machines, where a software takes designing
information from CASD database and convert them into other
program which controls and activate the manufacturing machines.
• Computers in Medical
Computer aided diagnostic machines are used to diagnose various types of
disease. It also helps in surgery and treatment. Eye testing, scanning of
internal parts of brain, by pass surgery, pathological tests are the
examples where computers are used effectively.
• Animation & Graphics
Specialized software like Corel Draw, Harvard graphics Photoshop, etc., can
be used to draw pictures and designs. It helps an artist to improve his
skill and reduces the time consumed when drawn manually.
• Military
• For the defense purposes in military computer plays an important role. A
guided missile fitted with its own computer that decides about the
target and path. Similarly system uses for processing data and image
display.
• Fighter planes are fitted with computerized system controls to decide
about range height etc. of the target.
Input Devices
• Keyboard
A computer keyboard is similar to a typewriter keyboard. It is an input
device. Data can be entered into a computer through the keyboard.
Usually it has 101 keys arranged in 5 groups
• Alphanumeric keys – in QWERTY layout (the first six letters on the top
row of the letters are Q,W,E,R,T,Y) with A-Z ,0-9 plus some more
characters.
• Modifier keys– In addition to letters and punctuation marks, the
alphanumeric keys include the modifier keys as they are used in
conjunction with other keys. E.g. Shift, Ctrl (control key), Alt (alternate
key).
• Function keys– The function keys (F1, F2….F12) are usually arranged in a
row along the top of the keyboard. They allow us to give the computer
commands.
• Cursor movement keys- Arrow keys which let us change the position of
cursor on the screen. In a word processing program, there is a mark on
the screen where characters we type will be entered, this is called
• Special purpose keys – Each of the special keys performs
a specialised function.
• Esc– Key is used to back up one level in a multilevel
environment, it can be used to close multiple opened
programs in reverse order.
• Print screen – This key copies an image of the screen’s
contents to the clipboard.
• Scroll lock – Scroll lock causes the cursor to remain
stationary on the screen and the document’s contents
move around it, as in MS-Excel.
• Pause– In some programs, the pause key can be used to
stop a command in progress.
• The numeric keypad usually located on the right side of
the keyboard looks like an adding machine with ten digits
• Mouse
Mouse is a pointing device used to position the pointer. The
pointer is an on-screen object usually an arrow, that is used
to select a text, menus, move files or interact with programs,
files or data that appear on screens. It also allows us to
create graphic elements on the screens, such as lines, curves
and freehand shapes. Clicking and drag-and-drop editing
technique is used with the mouse. Earlier, ball-mouse
connected via PS/2 port was used but now USB port
connected optical mouse is prevalent.
• Scanners
• Image scanners
Image scanners convert any printed image into electronic
image by shining light onto the image and sensing the
intensity of the reflection at every point. Bar code reader is
• Optical Character Recognition (OCR)
It is used to translate the image into text that we can
edit. It uses specialized OCR software.
• Optical Mark Reader (OMR)
These scanners are capable of recognizing a pre-
specified type of mark made by pencil or pen. They
are used in evaluation of answer sheets of objective
test.
• Magnetic Ink Character Recognition (MICR)
They are used in banking industry to process cheques.
Cheques have bank identification code and cheque
numbers in a special ink that is read by MICR devices.
• Touch Screens, Voice Recognition Devices are also
Output Devices
• Monitor
It is also called as screen. It is a soft copy output device. It is similar to
television. Earlier monochrome (Black & White) or Colour CRT
(Cathode Ray Tube) monitors were used but now LED & LCD
monitors are prevalent. We can see the input information supplied
to the computer as well as the results obtained after processing on
monitor. The computer screen is divided into rows and columns. The
number of rows and columns that can be displayed is known as the
resolution like 640 x 480, 1024 x 768, etc. The intersection of row
and column is called a pixel (Picture Element).
Following are the different types of monitors generally used with
computers
• LED (Light Emitting Diode) Monitor
• SVGA (Super Video Graphic Array) Monitor
• LCD (Liquid Crystal Diode) Monitor
• Printers
Printers are used for producing the hard copy output on paper. Printers can be
broadly classified into Impact Printers & Non-impact Printers.
• Impact Printers
• Dot Matrix Printer A printer that produces output by printing dots onto the
page. They are often inexpensive. They are available in 80 and 132 columns
with print speeds from 100 characters per second to 1200 characters per
second.
• Non- Impact Printers
• Ink jet Printer It uses nozzles which spray jets of ink onto the paper. The
operating cost of the ink jet is low and expensive maintenance is rare. The
only part that needs replacement is the ink cartridge, which typically costs
less. Its speed is to print 2-4 pages per minute.
• Laser Printer Laser printers are more expensive than inkjet printers. Their
print quality is higher and is faster. They use direct scanning of laser beam on
the roller which fuses ink to the paper.
• Plotters
Plotters are output devices, which plots big size drawings on to the sheets. They
are used in plotting of engineering drawings, architectural maps, design
• Storage Devices
• It is an important unit of computer. It is further divided into
primary and secondary memory. There is important difference
between address number and the contents of the address. The
contents stored may be any text, number or any thing but the
address at which they are stored is fixed.
• Primary Storage Devices
• A primary or internal storage section is in all computers and
consists of cache, processor register ROM & RAM.
• RAM (Random Access Memory)
• It provides random selection and usage of memory location to
store and retrieve data. It is also called read/write memory
because information can be read and can also be written into it.
It is a volatile memory; it gets erased as and when the computer
is switched off. Whenever a new data is stored, the previous
data is erased and new data takes place. It is present in
• ROM (Read Only Memory)
A read only memory (ROM) is one in which information is
permanently stored. The information from the memory can
only be read and it is not possible to write into it. It is non-
volatile, i.e. when the power supply is switched off, the
contents on ROM do not get erased, and they are permanent
and are written only by the manufacturer. The programs, which
are always required for running the machine, are stored in
ROM. The ROM usually contains the BIOS (Basic Input &
Output System) which checks the hardware for proper
functioning and in case of problem it stops booting of
computer and audio beeps are given. BIOS also load the
Operating System into the memory.
• Processor Registers
They are located in the CPU to load instructions for execution by
the CPU. They function with speed of CPU and hence are the
• Central Processing Unit (C.P.U)
• The Central Processing Unit (CPU) is responsible for interpreting
and executing most of the commands from the computer’s
hardware and software. It is often called the “brains” of the
computer. The CPU is also known as processor, microprocessor,
and central processor. The Central Processing Unit (C.P.U) can be
further divide into the following ways.
• Control Unit
• The control unit is the circuitry that controls the flow of
information through the processor, and coordinates the activities
of the other units within it. It generates signal as per which the
processing is done and is given in MHz/GHz (mega Hertz/ Giga
Hertz) .In a way, it is the “brain within the brain”, as it controls
what happens inside the processor, which in turn controls the rest
of the PC. The functions performed by the control unit vary
greatly by the internal architecture of the CPU, since the control
unit really implements this architecture.
