1. (1). Introduction of Computer :
Computer : It is an electronic device which processes given data to derive
the required and useful information. During the processing the computer
has to perform various functions like
(i) Accepting Instructions & data from the user.
(ii) Performing various arithmetic and Logical operations as per
Instructions given.
(iii) Presenting the Information or Output to the user
Characteristics of a Computer
The Characteristics which make computer indispensable are
1) Speed :- The computer is able to process the date and give the output
in fractions of seconds such that required information is given to the user
on time enabling the user to take right decisions on right time. A powerful
computer is capable of executing about 3 million calculations per second.
2) Accuracy :- Inspite of its high speed of processing, the computers
accuracy is consistently high enough which avoids any errors. If it all
there are errors, they are due to errors in instructions given by the
programmer.
3) Reliable :- The output generated by the computer is very reliable, but it
is reliable only when the data, which is passing as input to the computer
and the program, which gives instructions are correct and reliable.
4) Storage Capacity :- The computer has a provision to store large volumes
of data in the small storage devices, which have capacity to store huge
amounts of data and help the retrieval of data an easy task.
5) Versatile :- The computer perform three basic operations
1) It is capable to access and accept information through various
input-output devices from the user.
2) It performs basic Arithmetic and Logic operations on data as
desired.
3) It is capable to generate the desired output in the desired form.
6) Automation :- Once the instructions fed into computer it works
automatically without any human intervention until the completion of
execution of program until meets logical instructions to terminate the job.
7) Diligent :- The computer performance is consistent even to all extent of
more than 10 million calculations, it does each and every calculation with
same speed and accuracy.
Limitation of Computer :
1) Computer does not work on itself, it requires set of instructions to be
provided, else computer (Hardware) is waste.
2) Computer are not intelligent, they have to be instructed about each
and every step which they have to perform
3) Computers cannot take decisions on its own, one has to program
the computer to take an action if some conditional prevail.
4) Computers, unlike humans cannot learn by experience.
1. (2). The Computer Generations : The development of computers has
followed different steps in the terminology used and these steps of
technological differences are called as GENERATIONS in computer
terminology.
GENERATIONS OF COMPUTER
There are totally five generations of computers till today.
1. First Generation Computers (1950's) :
These computer which used vaccum tubes (valves) as major
electronic component the advantage of vaccum tubes technology is that it
made the advent of Electronic digital computer vaccum tubes were only
electronic devices available during those days which made computing
possible.
2. Second Generation Computers (1960's) :
With the development of Transistors and there use in circuits,
magnetic core for memory storage, the vaccum tubes are replaced by
transistors to arrive at 2nd generation of computers. The size of transistors
is much smaller when compared to vaccum tubes, they consume less
power, generated less heat and faster and reliable.
Advantages :
(1) Size of Computer has come down as well as power
consumption.
(2) The Cost of Computer reduced.
3.Third Generation Computers (1970's) :
The development of silicon chips, the third generation of computers came
into existence. These computers are used Integrated Circuits (IC's) of silicon
chips, in the place of transistors. Each of these IC's consist of large number
of chips in very small packages.
Advantage : The size of computers, cost, heat generation and power
consumption decreased to great extent, speed and reliability increased as
compared to previous generation. These machines used IC's with large
scale Integration (LSI).
4. Fourth Generation (1980's) :
The Computers belonging to these generations used Integrated
circuits with Very Large Scale Integration (VLSI).
Advantages :
1) These computers have high processing powers, low
maintenance, high reliability and very low power
consumption.
2) The size & cost of computers come down drastically
5. Fifth Generation (Late 1990's) :-
These computers use optic fibre technology to handle Artificial Intelligence,
expert systems, Robotics etc., these computers have very processing
speeds and are more reliable.
.Classification of Computers : Computers in general can be
classified into major categories based on.
(a) According to the purpose of the computer.
(b) According to the operation size of computer.
(a) Classification as per purpose of the computer :
Classification of digital computer as per the purpose of their use
1. General purpose digital computers.
2. Special purpose digital computer.
1. General Purpose digital computers : These computers are
theoretically used for any type of applications. These computers can be
used in solving a business Problem and also used to solve mathematical
equation with same accuracy and consistency. Most of the computer now
are general purpose digital computers. All the P.C's, which have become
household affair.
2. Special Purpose Computers : These digital computer are designed,
made and used for any specific job. These are usually used for those
purposes which are critical and need great accuracy and response like
Satellite launching weather forecasting etc.
(b) According to size and capabilities
1. Super Computers
2. Main frame Computer
3. Medium scale Computer
4. Mini Computers
5. Micro Computers.
(1) Super Computers : These computers are characterised as being the
fastest, with very high processing speed, very large size, most powerful.
There are widely used in complex scientific applications like processing
geological data, weather data, genetic engineering etc.
These computers with 16 microprocessors, will recognize words
upto length 64 bits and more. The speed of calculation is upto 1.2 billion
instructions/second, and they can take input from more than 1000 individual
work station.
Ex. PARAM developed in India.
(2) Mainframe Computers : These Computer will has capability to support
many peripheral devices and terminals, which can process several Million
Instructions / second (MIPS), as well which support 1000 remote systems,
these computers are mostly used for Railway reservation etc.
(3) Medium Scale (size) Computers : These computers are mini versions
of mainframe computers, they are relatively smaller than mainframes and
have less processing power than Mainframes their processing speed
support upto 200 remote systems.
(4) Mini Computers : These computer are smaller and less experience
than Mainframe and medium sized computers. They are relatively faster it
can support about 10-20 user terminals. These computers are generally
easy to use. They can handle database, statistical problems Accounting
etc.
(5) Micro Computer : These are the mostly used category of computes
called as personal computers (PC's). The word Micro suggests only the
size, but not the capacity. They are capable to do all input - output operations.
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