Type of Computers

Computers can be broadly classified by their speed and computing power.

PC (Personal Computer)
A PC can be defined as a small, relatively inexpensive computer designed for an individual
user. PCs are based on the microprocessor technology that enables manufacturers to put an
entire CPU on one chip. Businesses use personal computers for word processing, accounting,
desktop publishing, and for running spreadsheet and database management applications. At
home, the most popular use for personal computers is playing games and surfing the Internet.
Although personal computers are designed as single-user systems, these systems are
normally linked together to form a network. In terms of power, now-a-days high-end models
of the Macintosh and PC offer the same computing power and graphics capability as low-end
workstations by Sun Microsystems, Hewlett-Packard, and Dell.

Workstation
Workstation is a computer used for engineering applications (CAD/CAM), desktop
publishing, software development, and other such types of applications which require a
moderate amount of computing power and relatively high quality graphics capabilities.
Workstations generally come with a large, high-resolution graphics screen, large amount of
RAM, inbuilt network support, and a graphical user interface. Most workstations also have
mass storage device such as a disk drive, but a special type of workstation, called diskless
workstation, comes without a disk drive.
Common operating systems for workstations are UNIX and Windows NT. Like PC,
workstations are also single-user computers like PC but are typically linked together to form
a local-area network, although they can also be used as stand-alone systems.
Minicomputer
It is a midsize multi-processing system capable of supporting up to 250 users
simultaneously.

Mainframe
Mainframe is very large in size and is an expensive computer capable of supporting
hundreds or even thousands of users simultaneously. Mainframe executes many programs
concurrently and supports many simultaneous execution of programs.

Supercomputer
Supercomputers are one of the fastest computers currently available. Supercomputers are
very expensive and are employed for specialized applications that require immense
amount of mathematical calculations (number crunching).
For example, weather forecasting, scientific simulations, (animated) graphics, fluid
dynamic calculations, nuclear energy research, electronic design, and analysis of
geological data (e.g. in petrochemical prospecting).

Components of a Computer
All types of computers follow the same basic logical structure and perform the following
five basic operations for converting raw input data into information useful to their users.
Input Unit
This unit contains devices with the help of which we enter data into the computer. This
unit creates a link between the user and the computer. The input devices translate the
information into a form understandable by the computer.

CPU (Central Processing Unit)

CPU is considered as the brain of the computer. CPU performs all types of data processing
operations. It stores data, intermediate results, and instructions (program). It controls the
operation of all parts of the computer.
CPU itself has the following three components:
ALU (Arithmetic Logic Unit)
Memory Unit
Control Unit

Output Unit
The output unit consists of devices with the help of which we get the information from the
computer. This unit is a link between the computer and the users. Output devices translate
the computer's output into a form understandable by the users.

Components of the Central Processing Unit

Central Processing Unit (CPU) consists of the following features:
CPU is considered as the brain of the computer.
CPU performs all types of data processing operations.
It stores data, intermediate results, and instructions (program).
It controls the operation of all parts of the computer.

CPU itself has following three components.

Memory or Storage Unit
 Control Unit
ALU (Arithmetic Logic Unit)

Memory or Storage Unit

This unit can store instructions, data, and intermediate results. This unit supplies
information to other units of the computer when needed. It is also known as internal
storage unit or the main memory or the primary storage or Random Access Memory (RAM).
Its size affects speed, power, and capability. Primary memory and secondary memory are
two types of memories in the computer. Functions of the memory unit are:
It stores all the data and the instructions required for processing.
It stores intermediate results of processing.
It stores the final results of processing before these results are released to an
output device.
All inputs and outputs are transmitted through the main memory.

Control Unit
This unit controls the operations of all parts of the computer but does not carry out any
actual data processing operations.
Functions of this unit are:
It is responsible for controlling the transfer of data and instructions among other
units of a computer.
It manages and coordinates all the units of the computer.
It obtains the instructions from the memory, interprets them, and directs the
operation of the computer.
It communicates with Input/Output devices for transfer of data or results from
storage.
It does not process or store data.

ALU (Arithmetic Logic Unit)

This unit consists of two subsections namely,
Arithmetic Section
Logic Section
Arithmetic Section
Function of arithmetic section is to perform arithmetic operations like addition, subtraction,
multiplication, and division. All complex operations are done by making repetitive use of
the above operations.
Logic Section
Function of logic section is to perform logic operations such as comparing, selecting,
matching, and merging of data.
 Input Devices
Following are some of the important input devices which are used in a computer:
Keyboard
Mouse
Joy Stick
Light pen
Track Ball
Scanner
Graphic Tablet
Microphone
Magnetic Ink Card Reader (MICR)
Optical Character Reader (OCR)
Bar Code Reader
Optical Mark Reader (OMR)

Keyboard
Keyboard is the most common and very popular input device which helps to input data to
the computer. The layout of the keyboard is like that of traditional typewriter, although
there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or
108 keys are also available for Windows and Internet.

The keys on the keyboard are as follows:

Mouse
Mouse is the most popular pointing device. It is a very famous cursor-control device having
a small palm size box with a round ball at its base, which senses the movement of the
mouse and sends corresponding signals to the CPU when the mouse buttons are pressed.
Generally, it has two buttons called the left and the right button and a wheel is present
between the buttons. A mouse can be used to control the position of the cursor on the
screen, but it cannot be used to enter text into the computer.

Advantages
Easy to use
Not very expensive
Moves the cursor faster than the arrow keys of the keyboard

Joystick
Joystick is also a pointing device, which is used to move the cursor position on a monitor
screen. It is a stick having a spherical ball at its both lower and upper ends. The lower
spherical ball moves in a socket. The joystick can be moved in all four directions.
The function of the joystick is similar to that of a mouse. It is mainly used in Computer
Aided Designing (CAD) and playing computer games.

Light Pen
Light pen is a pointing device similar to a pen. It is used to select a displayed menu item
or draw pictures on the monitor screen. It consists of a photocell and an optical system
placed in a small tube.
When the tip of a light pen is moved over the monitor screen and the pen button is pressed,
its photocell sensing element detects the screen location and sends the corresponding
signal to the CPU.

Track Ball
Track ball is an input device that is mostly used in notebook or laptop computer, instead
of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the
pointer can be moved.
Since the whole device is not moved, a track ball requires less space than a mouse. A
track ball comes in various shapes like a ball, a button, or a square.

Scanner
Scanner is an input device, which works more like a photocopy machine. It is used when
some information is available on paper and it is to be transferred to the hard disk of the
computer for further manipulation.
Scanner captures images from the source which are then converted into a digital form that
can be stored on the disk. These images can be edited before they are printed.

Digitizer
Digitizer is an input device which converts analog information into digital form. Digitizer
can convert a signal from the television or camera into a series of numbers that could be
stored in a computer. They can be used by the computer to create a picture of whatever
the camera had been pointed at.
Digitizer is also known as Tablet or Graphics Tablet as it converts graphics and pictorial
data into binary inputs. A graphic tablet as digitizer is used for fine works of drawing and
image manipulation applications.

Microphone
Microphone is an input device to input sound that is then stored in a digital form.
The microphone is used for various applications such as adding sound to a multimedia
presentation or for mixing music.

Magnetic Ink Card Reader (MICR)

MICR input device is generally used in banks as there are large number of cheques to be
processed every day. The bank's code number and cheque number are printed on the
cheques with a special type of ink that contains particles of magnetic material that are
machine readable.
This reading process is called Magnetic Ink Character Recognition (MICR). The main
advantages of MICR is that it is fast and less error prone.

Optical Character Reader (OCR)

OCR is an input device used to read a printed text.
OCR scans the text optically, character by character, converts them into a machine
readable code, and stores the text on the system memory.

Bar Code Readers

Bar Code Reader is a device used for reading bar coded data (data in the form of light and
dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc.
It may be a handheld scanner or may be embedded in a stationary scanner.
Bar Code Reader scans a bar code image, converts it into an alphanumeric value, which is
then fed to the computer that the bar code reader is connected to.

Optical Mark Reader (OMR)

OMR is a special type of optical scanner used to recognize the type of mark made by pen
or pencil. It is used where one out of a few alternatives is to be selected and marked.
It is specially used for checking the answer sheets of examinations having multiple choice
questions.

Output Devices
Following are some of the important output devices used in a computer.
Monitors
Graphic Plotter
Printer
Monitors
Monitors, commonly called as Visual Display Unit (VDU), are the main output device of
a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular
form. The sharpness of the image depends upon the number of pixels.
There are two kinds of viewing screen used for monitors.
Cathode-Ray Tube (CRT)
Flat-Panel Display

Cathode-Ray Tube (CRT) Monitor

The CRT display is made up of small picture elements called pixels. The smaller the pixels,
the better the image clarity or resolution. It takes more than one illuminated pixel to form
a whole character, such as the letter ‘e’ in the word help.
A finite number of characters can be displayed on a screen at once. The screen can be
divided into a series of character boxes - fixed location on the screen where a standard
character can be placed. Most screens are capable of displaying 80 characters of data
horizontally and 25 lines vertically.
There are some disadvantages of CRT:
Large in Size
High power consumption

Flat-Panel Display Monitor

The flat-panel display refers to a class of video devices that have reduced volume, weight
and power requirement in comparison to the CRT. You can hang them on walls or wear
them on your wrists. Current uses of flat-panel displays include calculators, video games,
monitors, laptop computer, and graphics display.
The flat-panel display is divided into two categories:
Emissive Displays - Emissive displays are devices that convert electrical energy
into light. For example, plasma panel and LED (Light-Emitting Diodes).
Non-Emissive Displays - Non-emissive displays use optical effects to convert
sunlight or light from some other source into graphics patterns. For example, LCD
(Liquid-Crystal Device).

Printers
Printer is an output device, which is used to print information on paper.
There are two types of printers:
Impact Printers
Non-Impact Printers

Impact Printers
Impact printers print the characters by striking them on the ribbon, which is then pressed
on the paper.
Characteristics of Impact Printers are the following:
Very low consumable costs
Very noisy
 Useful for bulk printing due to low cost
There is physical contact with the paper to produce an image
These printers are of two types -
Character printers
Line printers

Character Printers
Character printers are the printers which print one character at a time.
These are further divided into two types:
Dot Matrix Printer (DMP)
Daisy Wheel

Dot Matrix Printer

In the market, one of the most popular printers is Dot Matrix Printer. These printers are
popular because of their ease of printing and economical price. Each character printed is
in the form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7
or 9*9) which come out to form a character which is why it is called Dot Matrix Printer.
Advantages
Inexpensive
Widely Used
Other language characters can be printed

Disadvantages
Slow Speed
Poor Quality

Daisy Wheel
Head is lying on a wheel and pins corresponding to characters are like petals of Daisy
(flower) which is why it is called Daisy Wheel Printer. These printers are generally used
for word-processing in offices that require a few letters to be sent here and there with
very nice quality.
Advantages
More reliable than DMP
Better quality
Fonts of character can be easily changed
Disadvantages
Slower than DMP
Noisy
More expensive than DMP

Line Printers
Line printers are the printers which print one line at a time.
These are of two types -
Drum Printer
 Chain Printer

Drum Printer
This printer is like a drum in shape hence it is called drum printer. The surface of the drum
is divided into a number of tracks. Total tracks are equal to the size of the paper, i.e. for
a paper width of 132 characters, drum will have 132 tracks. A character set is embossed
on the track. Different character sets available in the market are 48 character set, 64 and
96 characters set. One rotation of drum prints one line. Drum printers are fast in speed
and can print 300 to 2000 lines per minute.
Advantages
Very high speed
Disadvantages
Very expensive
Characters fonts cannot be changed

Chain Printer
In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard
character set may have 48, 64, or 96 characters.
Advantages
Character fonts can easily be changed.
Different languages can be used with the same printer.
Disadvantages
Noisy

Non-impact Printers
Non-impact printers print the characters without using the ribbon. These printers print a
complete page at a time, thus they are also called as Page Printers.
These printers are of two types -
Laser Printers
Inkjet Printers
Characteristics of Non-impact Printers
Faster than impact printers
They are not noisy
High quality
Supports many fonts and different character size

Laser Printers
These are non-impact page printers. They use laser lights to produce the dots needed to
form the characters to be printed on a page.
Advantages
Very high speed
Very high quality output
Good graphics quality
Supports many fonts and different character size
Disadvantages
Expensive
Cannot be used to produce multiple copies of a document in a single printing

Inkjet Printers
Inkjet printers are non-impact character printers based on a relatively new technology.
They print characters by spraying small drops of ink onto paper. Inkjet printers produce
high quality output with presentable features.
They make less noise because no hammering is done and these have many styles of
printing modes available. Color printing is also possible. Some models of Inkjet printers
can produce multiple copies of printing also.
Advantages
High quality printing
More reliable
Disadvantages
Expensive as the cost per page is high
Slow as compared to laser printer