INTRODUCTION COMPUTER
WHAT IS A COMPUTER?
Computer
is an electronic device. As mentioned in the introduction it can do arithmetic
calculations faster. But as you will see later it does much more than that. Which
works automatic and quite fast? computer is a machine capable of solving
problems and manipulating data. It accepts data, processes the data by doing
some mathematical and logical operations and gives us the desired output.
CHARACTERISTICS OF COMPUTER
Speed, accuracy, diligence, versatility and memory.
Speed
As you know computer can work
very fast. It takes only few seconds for calculations that we take hours to
complete. Suppose you are asked to calculate the average monthly income of one
thousand persons in your neighborhood. How long will it take for you to do
this? One day, two days or one week? Do you know your small computer can finish
this work in few seconds?
You will be surprised to know
that computer can perform millions (1,000,000) of instructions and even more
per second. Mille seconds, microsecond and nano-second
Accuracy
Suppose someone calculates
faster but commits a lot of errors in computing. Such result is useless. There
is another aspect. Computer shows accuracy or correctness in computing.
The degree of accuracy of computer
is very high and every calculation is performed with the same accuracy. The
accuracy level is determined on the basis of design of computer. The errors in
computer are due to human and inaccurate data.
Diligence
A computer is free from
tiredness, lack of concentration, fatigue, etc. It can work for hours without
creating any error. If millions of calculations are to be performed, a computer
will perform every calculation with the same accuracy. Due to this capability
it overpowers human being in routine type of work.
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.
Memory (Power of Remembering)
Computer has the power of
storing any amount of information or data. Any information can be stored and
recalled as long as you require it, for any numbers of years. It depends
entirely upon you how much data you want to store in a computer and when to
lose or retrieve these data.
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.
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 floppies, which can be kept outside your
computer and can be carried to other computers.
HISTORY OF COMPUTER
History of computer could be
traced back to the effort of man to count large numbers. This process of
counting of large numbers generated various systems of numeration like Greek
system of numeration, Roman system of numeration and Indian system of
numeration. Out of these the Indian system of numeration has been accepted
universally. It is the basis of modern decimal system of numeration (0, 1, 2,
3, 4, 5, 6, 7, 8, 9). The computer does not understand the decimal system and
uses binary system of numeration for processing.
It took over generations for
early man to build mechanical devices for counting large numbers. The first
calculating device called ABACUS was developed by the Egyptian and Chinese
people.
The word ABACUS means
calculating board. It consisted of sticks in horizontal positions on which were
inserted sets of pebbles. A modern form of ABACUS is given in Fig. 1.2. It has
a number of horizontal bars each having ten beads. Horizontal bars represent
units, tens, hundreds, etc.
Napier’s bones
English mathematician John Napier
built a mechanical device for the purpose of multiplication in 1617 A D. The
device was known as Napier’s bones.
Slide Rule
English mathematician Edmund Gunter
developed the slide rule. This machine could perform operations like addition,
subtraction, multiplication, and division. It was widely used in Europe in 16th
century.
Pascal's Adding and Subtractory Machine
You might have heard the name
of Blaise Pascal.
He developed a machine at the age of 19 that could add and subtract. The
machine consisted of wheels, gears and cylinders.
Leibniz’s Multiplication and Dividing
Machine
The German philosopher and
mathematician Gottfried Leibniz built around 1673 a mechanical device that
could both multiply and divide.
Babbage’s Analytical Engine
It was in
the year 1823 that a famous English man Charles Babbage built a mechanical
machine to do complex mathematical calculations. It was called difference
engine. Later he developed a general-purpose calculating machine called analytical
engine. You should know that Charles Babbage is called the father of computer.
Mechanical and Electrical Calculator
In the beginning of 19th
century the mechanical calculator was developed to perform all sorts of
mathematical calculations. Up to the 1960s it was widely used. Later the
rotating part of mechanical calculator was replaced by electric motor. So it
was called the electrical calculator.
Modern Electronic Calculator
The electronic calculator
used in 1960 s was run with electron tubes, which was quite bulky. Later it was
replaced with transistors and as a result the size of calculators became too
small.
The modern electronic
calculator can compute all kinds of mathematical computations and mathematical
functions. It can also be used to store some data permanently. Some calculators
have in-built programs to perform some complicated calculations.
Vacuum tube, transistor, IC
COMPUTER GENERATIONS
You know that the evolution
of computer started from 16th century and resulted in the form that we see
today. The present day computer, however, has also undergone rapid change
during the last fifty years. This period, during which the evolution of
computer took place, can be divided into five distinct phases known as
Generations of Computers. Each phase is distinguished from others on the basis
of the type of switching circuits used.
First Generation Computers
First generation computers
used Thermion valves. These computers were large in size and writing programs
on them was difficult. Some of the computers of this generation were:
ENIAC: It was the first electronic computer built in 1946 at University of
Pennsylvania, USA by John Eckert and John Mauchy. It was named Electronic
Numerical Integrator and Calculator (ENIAC). The ENIAC was 3050 feet long,
weighed 30 tons, contained 18,000 vacuum tubes, 70,000 registers, 10,000
capacitors and required 150,000 watts of electricity. Today your favorite
computer is many times as powerful as ENIAC, still size is very small.
EDVAC: It stands for Electronic Discrete Variable Automatic Computer and was
developed in 1950. The concept of storing data and instructions inside the
computer was introduced here. This allowed much faster operation since the
computer had rapid access to both data and instructions. The other advantages
of storing instruction was that computer could do logical decision internally.
Other Important Computers of First
Generation
EDSAC: It stands for Electronic Delay Storage Automatic Computer and was
developed by M.V. Wilkes at Cambridge University in 1949.
UNIVAC-I: Eckert and Mauchly invented it in 1951 by Universal Accounting
Computer setup.
Limitations of First Generation Computer
Followings are the major drawbacks of First generation computers.
The operating speed was quite
slow.
Power consumption was very
high.
It required large space for
installation.
The programming capability
was quite low.
Around 1955 a device called
Transistor replaced the bulky electric tubes in the first generation computer.
Transistors are smaller than electric tubes and have higher operating speed.
They have no filament and require no heating. Manufacturing cost was also very
low. Thus the size of the computer got reduced considerably.
It is in the second
generation that the concept of Central Processing Unit (CPU), memory,
programming language and input and output units were developed. The programming
languages such as COBOL, FORTRAN were developed during this period.
Some of the computers of the Second
Generation were
IBM 1620: Its size was
smaller as compared to First Generation computers and mostly used for
scientific purpose.
IBM 1401: Its size was small
to medium and used for business applications.
CDC 3600: Its size was large
and is used for scientific purposes.
Third Generation Computers
The third generation
computers were introduced in 1964. They used Integrated Circuits (ICs). These
ICs are popularly known as Chips. A single IC has many transistors, registers
and capacitors built on a single thin slice of silicon. So it is quite obvious
that the size of the computer got further reduced. Some of the computers
developed during this period were IBM-360, ICL-1900, IBM-370, and VAX-750.
Higher level language such as BASIC (Beginners All purpose Symbolic Instruction
Code) was developed during this period.
Computers of this generation
were small in size, low cost, large memory and processing speed is very high.
Fourth Generation Computers
The present day computers
that you see today are the fourth generation computers that started around
1975. It uses large scale Integrated Circuits (LSIC) built on a single silicon
chip called microprocessors. Due to the development of microprocessor it is
possible to place computer’s central processing unit (CPU) on single chip.
These computers are called microcomputers. Later very large scale Integrated
Circuits (VLSIC) replaced LSICs.
Thus the computer which was
occupying a very large room in earlier days can now be placed on a table. The
personal computer (PC) that you see in your school is a Fourth Generation
Computer.
Fifth Generation Computer
The computers of 1990s are
said to be Fifth Generation computers. The speed is extremely high in fifth
generation computer. Apart from this it can perform parallel processing. The
concept of Artificial intelligence has been introduced to allow the computer to
take its own decision. It is still in a developmental stage.
TYPES OF COMPUTERS
Now let us discuss the
varieties of computers that we see today. Although they belong to the fifth
generation they can be divided into different categories depending upon the
size, efficiency, memory and number of users. Broadly they can be divided it to
the following categories.
Microcomputer: Microcomputer is at the lowest end of the computer
range in terms of speed and storage capacity. Its CPU is a microprocessor. The
first microcomputers were built of 8-bit microprocessor chips. The most common
application of personal computers (PC) is in this category. The PC supports a
number of input and output devices. An improvement of 8-bit chip is 16-bit and
32-bit chips. Examples of microcomputer are IBM PC, PC-AT .
Mini Computer: This is designed to support more than one user at a
time. It possesses large storage capacity and operates at a higher speed. The
mini computer is used in multi-user system in which various users can work at
the same time. This type of computer is generally used for processing large
volume of data in an organisation. They are also used as servers in Local Area
Networks (LAN).
Mainframes: These types of computers are generally 32-bit
microprocessors. They operate at very high speed, have very large storage
capacity and can handle the work load of many users. They are generally used in
centralized databases. They are also used as controlling nodes in Wide Area Networks
(WAN). Example of mainframes are DEC, ICL and IBM 3000 series.
Supercomputer: They are the fastest and most expensive machines.
They have high processing speed compared to other computers. They have also
multiprocessing technique. One of the ways in which supercomputers are built is
by interconnecting hundreds of microprocessors. 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.
BASIC COMPUTER OPERATIONS
A computer as shown in Fig.
2.1 performs basically five major operations or functions irrespective of their
size and make.
1) It accepts data or instructions by
way of input
2) It stores data
3) It can process data as required by
the user
4) It gives results in the form of
output, and
5) It controls all operations inside a
computer. We discuss below each of these operations.
Input: This is the process of entering data and programs in to the computer
system. You should know that computer is an electronic machine like any other
machine which takes as inputs raw data and performs some processing giving out
processed data. Therefore, the input unit takes data from us to the computer in
an organized manner for processing.
Basic computer Operations
Storage:
The process of saving data and instructions permanently is known as storage.
Data has to be fed into the system before the actual processing starts. It is
because the processing speed of Central Processing Unit (CPU) is so fast that
the data has to be provided to CPU with the same speed. Therefore the data is
first stored in the storage unit for faster access and processing. This storage
unit or the primary storage of the computer system is designed to do the above
functionality. It provides space for storing data and instructions.
The storage unit performs the following
major functions:
All data and instructions are
stored here before and after processing.
Intermediate results of
processing are also stored here.
Processing: The task of performing operations like arithmetic and
logical operations is called processing. The Central Processing Unit (CPU)
takes data and instructions from the storage unit and makes all sorts of
calculations based on the instructions given and the type of data provided. It
is then sent back to the storage unit.
Output: This is the process of producing results from the data for getting
useful information. Similarly the output produced by the computer after
processing must also be kept somewhere inside the computer before being given
to you in human readable form. Again the output is also stored inside the
computer for further processing.
Control: The manner how instructions are executed and the above operations are
performed. Controlling of all operations like input, processing and output are
performed by control unit. It takes care of step by step processing of all
operations inside the computer.
FUNCTIONAL UNITS
In order to carry out the
operations mentioned in the previous section the computer allocates the task
between its various functional units. The computer system is divided into three
separate units for its operation. They are 1) arithmetic logical unit, 2)
control unit, and 3) central processing unit.
Arithmetic Logical Unit (ALU)
After you enter data through
the input device it is stored in the primary storage unit. The actual
processing of the data and instruction are performed by Arithmetic Logical Unit.
The major operations performed by the ALU are addition, subtraction,
multiplication, division, logic and comparison. Data is transferred to ALU from
storage unit when required. After processing the output is returned back to
storage unit for further processing or getting stored.
Control Unit (CU)
The next component of
computer is the Control Unit, which acts like the supervisor seeing that things
are done in proper fashion. The control unit determines the sequence in which
computer programs and instructions are executed. Things like processing of
programs stored in the main memory, interpretation of the instructions and
issuing of signals for other units of the computer to execute them. It also
acts as a switch board operator when several users access the computer
simultaneously. Thereby it coordinates the activities of computer’s peripheral
equipment as they perform the input and output. Therefore it is the manager of
all operations mentioned in the previous section.
Central Processing Unit (CPU)
The
ALU and the CU of a computer system are jointly known as the central processing
unit. You may call CPU as the brain of any computer system. It is just like
brain that takes all major decisions, makes all sorts of calculations and
directs different parts of the computer functions by activating and controlling
the operations.
Computer Architecture
Personal Computer
Configuration
Physical components that make the computer
work. These are
Central Processing Unit (CPU)
Computer Memory (RAM and ROM)
Data bus
Ports
Motherboard
Hard disk
Output Devices
Input Devices
All these components are
inter-connected for the personal computer to work.
MEMORY SYSTEM IN A COMPUTER
There are two kinds of
computer memory: primary and secondary.
Primary memory is accessible directly by the processing unit. RAM is
an example of primary memory. As soon as the computer is switched off the
contents of the primary memory is lost. You can store and retrieve data much
faster with primary memory compared to secondary memory.
Secondary memory such as floppy disks, magnetic disk, etc., is located
outside the computer. Primary memory is more expensive than secondary memory.
Because of this the size of primary memory is less than that of secondary
memory. We will discuss about secondary memory later on.
Computer memory is used to
store two things:
i)
instructions to
execute a program and
ii)
Data. When the computer is doing any
job, the data that have to be processed are stored in the primary memory. This
data may come from an input device like keyboard or from a secondary storage
device like a floppy disk.
As program or the set of
instructions is kept in primary memory, the computer is able to follow
instantly the set of instructions. For example, when you book ticket from
railway reservation counter, the computer has to follow the same steps: take the request, check the
availability of seats, calculate fare, and wait for money to be paid, store the
reservation and get the ticket printed out. The programme containing
these steps is kept in memory of the computer and is followed for each request.
But inside the computer, the
steps followed are quite different from what we see on the monitor or screen.
In computer’s memory both programs and data are stored in the binary form.
You have already been
introduced with decimal
number system that is the numbers 0 to 9. The binary system has only two values 0 and 1.
These are called bits. As human beings we all understand decimal system but the
computer can only understand binary system. It is because a large number of integrated
circuits inside the computer can be considered as switches, which can be
made ON, or OFF. If a switch is ON it is considered 1 and if it is OFF it is 0.
A number of switches in different states will give you a message like this:
110101....10. So the computer takes input in the form of 0 and 1 and gives
output in the form 0 and 1 only. Is it not absurd if the computer gives outputs
as 0’s & 1’s only? But you do not have to worry about. Every number in
binary system can be converted to decimal system and vice versa; for example,
1010 meaning decimal 10. Therefore it is the computer that takes information or
data in decimal form from you, convert it in to binary form, process it
producing output in binary form and again convert the output to decimal form.
The primary memory as you
know in the computer is in the form of IC’s (Integrated Circuits). These circuits are
called Random
Access Memory (RAM). Each of RAM’s locations stores one byte of
information. (One byte is equal to 8 bits). A bit is an acronym
for binary digit, which stands for one binary piece of information. This can be
either 0 or 1. The Primary or internal storage section is made up of several
small storage locations (ICs) called cells. Each of these cells can store a fixed number of bits called word
length.
Each cell has a unique number
assigned to it called the address of the cell and it is used to identify the
cells. The address
starts at 0 and goes up to (N-1). You should know that the memory is
like a large cabinet containing as many drawers as there are addresses on
memory. Each drawer contains a word and the address is written on outside of
the drawer.
You know that each cell of
memory contains one character or 1 byte of data. So the capacity is defined in
terms of byte or words. Thus 64 kilobyte (KB) memory is capable of storing 64 1024 =
32,768 bytes. (1 kilobyte is 1024 bytes). A memory size ranges from
few kilobytes in small systems to several thousand kilobytes in large mainframe
and super computer. In your personal computer you will find memory capacity in
the range of 64
KB, 4 MB, 8 MB and even 16 MB (MB = Million bytes).
The following
terms related to memory of a computer are discussed below:
Random Access Memory (RAM): The primary storage is referred to as random access
memory (RAM) because it is possible to randomly select and use any location of
the memory directly store and retrieve data. It takes same time to any address
of the memory as the first address. It is also called read/write memory. The
storage of data and instructions inside the primary storage is temporary.
It disappears from RAM as
soon as the power to the computer is switched off. The memories, which
loose their content on failure of power supply, are known as volatile memories .So now
we can say that RAM is volatile memory.
Read Only Memory (ROM): There is another memory in computer, which is called
Read Only Memory (ROM). Again it is the ICs inside the PC that form the ROM.
The storage of program and data in the ROM is permanent. The ROM stores some
standard processing programs supplied by the manufacturers to operate the
personal computer. The ROM can only be read by the CPU but it cannot be changed. The basic
input/output program is stored in the ROM that examines and initializes various
equipment attached to the PC when the switch is made ON. The
memories, which do
not loose their content on failure of power supply, are known as non-volatile
memories. ROM is non-volatile memory.
PROM There is another type of
primary memory in computer, which is called Programmable Read Only Memory
(PROM). You know that it is not possible to modify or erase programs stored in ROM,
but it is possible for you to store your program in PROM chip. Once the
programmes are written it cannot be changed and remain intact even if power is switched off.
Therefore programs or instructions written in PROM or ROM cannot be erased or changed.
EPROM: This stands for Erasable
Programmable Read Only Memory, which overcome the problem of PROM
& ROM. EPROM chip can be programmed time and again by erasing the information stored
earlier in it. Information stored in EPROM exposing the chip for some time
ultraviolet light and it erases chip is reprogrammed using a special
programming facility. When the EPROM is in use information can only
be read.
Cache Memory: The speed of CPU is extremely high compared to the
access time of main memory. Therefore the performance of CPU decreases due to
the slow speed of main memory. To decrease the mismatch in operating speed, a small memory chip
is attached between CPU and Main memory whose access time is very close to the
processing speed of CPU. It is called CACHE memory. CACHE memories
are accessed much
faster than conventional RAM. It is used to store programs or data
currently being executed or temporary data frequently used by the CPU. So each
memory makes main memory to be faster and larger than it really is. It is also very expensive to
have bigger size of cache memory and its size is normally kept small.
Registers: The CPU processes data and instructions with high
speed, there is also movement of data between various units of computer. It is
necessary to transfer the processed data with high speed. So the computer uses
a number of special
memory units called registers. They are not part of the main memory
but they store
data or information temporarily and pass it on as directed by the
control unit.
SECONDARY
STORAGE
You are now clear that the
operating speed of primary memory or main memory should be as fast as possible
to cope up with the CPU speed. These high-speed storage devices are very
expensive and hence the cost per bit of storage is also very high. Again the
storage capacity of the main memory is also very limited. Often it is necessary
to store hundreds of millions of bytes of data for the CPU to process.
Therefore additional memory is required in all the computer systems. This memory is
called auxiliary memory or secondary storage.
In this type of memory the cost per
bit of storage is low. However, the operating speed is slower than that of the primary
storage. Huge
volume of data are stored here on permanent basis and transferred to
the primary storage as and when required. Most widely used secondary storage devices are magnetic
tapes and magnetic disk.
Magnetic Tape: Magnetic tapes are used for large computers like mainframe
computers where large volume of data is stored for a longer time. In
PC also you can use tapes in the form of cassettes. The cost of storing data in
tapes is inexpensive.
Tapes consist of magnetic
materials that store data permanently. It can be 12.5 mm to 25 mm
wide plastic film-type and 500 meter to 1200 meter long which
is coated with magnetic material. The deck is connected to the central
processor and information is fed into or read from the tape through the
processor. It similar to
cassette tape recorder.
Advantages of Magnetic Tape:
Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to hold
800, 1600 or 6250 characters in each inch of its length. The maximum capacity
of such tape is 180 million characters. Thus data are stored much more
compactly on tape.
Economical: The cost of storing characters is very less as
compared to other storage devices.
Fast:
Copying of data is easier and fast.
Long term Storage and Re-usability: Magnetic tapes can be used for long term storage and
a tape can be used repeatedly without loss of data.
Magnetic Disk: You might have seen the gramophone record, which is circular
like a disk and coated with magnetic material. Magnetic disks used in computer
are made on the same principle. It rotates with very high speed inside the
computer drive. Data
is stored on both the surface of the disk. Magnetic disks are most popular for
direct access storage device. Each disk consists of a number of invisible
concentric circles called tracks. Information is recorded on tracks of a disk surface in
the form of tiny magnetic spots. The presence of a magnetic spot
represents one bit and its absence represents zero bit. The information stored
in a disk can be
read many times without affecting the stored data. So the reading
operation is non-destructive. But if you want to write a new data, then the
existing data is erased from the disk and new data is recorded.
Floppy Disk: It is similar to magnetic disk discussed above. They are 5.25 inch
or 3.5 inch in diameter. They come in single or double density and
recorded on one
or both surface of the diskette. The capacity of a 5.25-inch floppy is
1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes. It is cheaper
than any other storage devices and is portable. The floppy is a low cost device particularly suitable for
personal computer system.
Floppy
Disk
Optical Disk:
With every new application
and software there is greater demand for memory capacity. It is the necessity
to store large volume of data that has led to the development of optical disk
storage medium.
Optical disks can be divided into the
following categories:
Compact Disk/
Read Only Memory (CD-ROM): CD-ROM disks are
made of reflective metals. CD-ROM is written during the process of manufacturing by
high power laser beam. Here the storage density is very high, storage cost is very low
and access time is
relatively fast. Each disk is approximately 4 1/2 inches in diameter and can hold over 600
MB of data. As the CD-ROM can be read only we cannot write or make changes
into the data contained in it.
Write Once,
Read Many (WORM): The
inconvenience that we cannot write anything in to a CD-ROM is avoided in WORM.
A WORM allows the user to write data permanently on to the disk. Once the
data is written it can never be erased without physically damaging the disk.
Here data
can be recorded from keyboard, video scanner, OCR equipment and other devices.
The advantage of WORM is that it can store vast amount of data amounting to gigabytes (109
bytes). Any document in a WORM can be accessed very fast, say less than 30
seconds.
Erasable
Optical Disk: These are optical disks
where data can
be written, erased and re-written. This also applies a laser beam to write
and re-write the data. These disks may be used as alternatives to
traditional disks. Erasable optical disks are based on a technology known as
magnetic optical (MO). To write a data bit on to the erasable optical disk the
MO drive's laser beam heats a tiny, precisely defined point on the disk's
surface and magnetises it.
INPUT OUTPUT
DEVICES
A computer is only useful
when it is able to communicate with the external environment. When you work
with the computer you feed your data and instructions through some devices to the
computer. These devices are called Input devices. Similarly computer
after processing gives output through other devices called output devices.
For a particular application
one form of device is more desirable compared to others. We will discuss
various types of I/O devices that are used for different types of applications.
They are also known as peripheral devices because they surround the CPU and
make a communication between computer and the outer world.
Input Devices
Input devices are necessary
to convert our information or data in to a form which can be understood by the
computer. A good input device should provide timely, accurate and useful data
to the main memory of the computer for processing followings are the most
useful input devices.
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. A typical keyboard used in a computer is shown in
Fig. 2.6. You have to press correct combination of keys to input data. The
computer can recognise
the electrical signals corresponding to the correct key combination and
processing is done accordingly.
Mouse: - Mouse is an input device shown in Fig. 2.7 that is
used with your personal computer. It rolls on a small ball 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.
Scanner: The keyboard can input only text through keys
provided in it. If we want to input a picture the keyboard cannot do that.
Scanner is an optical device that can input any graphical matter and display it
back. The common
optical scanner devices are Magnetic Ink Character Recognition (MICR), Optical
Mark Reader (OMR) and Optical Character Reader (OCR).
Magnetic Ink Character Recognition (MICR): - This is widely used by banks to process large volumes
of cheques and drafts. Cheques are put inside the MICR. As they enter the
reading unit the cheques pass through the magnetic field which causes the read
head to recognise the character of the cheques.
Optical Mark Reader (OMR): This technique is used when students have appeared in
objective type tests and they had to mark their answer by darkening a square or
circular space by pencil. These answer sheets are directly fed to a computer
for grading where OMR is used.
Optical Character Recognition (OCR): - This technique unites the direct reading of any
printed character. Suppose you have a set of hand written characters on a piece
of paper. You put it inside the scanner of the computer. This pattern is
compared with a site of patterns stored inside the computer. Whichever pattern
is matched is called a character read. Patterns that cannot be identified are
rejected. OCRs are expensive though better the MICR.
Output Devices
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.
Terminals: It is a very popular interactive input-output unit. It can be divided
into two types: hard copy terminals and soft copy terminals. A hard copy
terminal provides a printout on paper whereas soft copy terminals provide
visual copy on monitor. A terminal when connected to a CPU sends instructions
directly to the computer. Terminals are also classified as dumb terminals or
intelligent terminals depending upon the work situation.
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 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.
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