All though the modern electronic computer are only a
recent phenomenon, but the ideas & devices leading to the advent of the
computer far back in the history.
In 450 BC, a machine is developed
whose name is ABACUS. It is the first known calculating device. It is invented
by the chiness. In 1642, the well known French scientist and mathematician,
Blaise Pascal invented the first machine which could add & carry digits
automatically. This machine was known as adding
machine. In 1692, Baron G. Wilhelm von Leibniz of Germany improves upon Pascal’s
machine & introduces a mechanism to carry out automatic multiplication of
numbers. This machine is known as multiplying
machine. In 1833, Charles Babbage, an English mathematician, develop a
mechanical calculating device, called difference engine. In 1942, a group of
scientist devised the Mark 1 which was the first electromecanical calculator in
the world. In 1944, scientist of Moore School of Electrical Engineering, University of Pennsylvania, USA, broad out ENIAC. It was the first electronic calculator. In 1947, the
scientists of Cambridge University,
UK, broad out EDSAC. It was the first electronic
computer in the world. In 1951, Sperry Rand Corporation of USA introduced the first commercial
computer to the world & named it Universal
Automatic Computer (UNIVAC 1)
Following are the various
generations of the computer:
First
Generation (1942-1955)
First generation computers use the
vacuum tubes technology. It was the
only high speed electronic switching device available in those days. Their
memory capacity was between 10,000 to 20,000 characters. The instructions
written in these computers in machine and assembly languages. Its internal
operating speed was in milli seconds (10-3s). Its external speed was
thousands of instructions per second.
Second
Generation (1955-1964)
Second generation computers use
the transistors in place of vacuum
tubes. They used magnetic cores for main memory, and magnetic disk and tape as
secondary storage media. They were more powerful, more reliable, less
expensive, smaller and cooler to operate than the first generation computers.
Its memory capacity was 4000 to 64,000 characters. Its internal operating speed
was micro seconds (10-6s). Its external speed was up to 1 lakh
instructions per second.
Third
Generation (1964-1975)
Third generation computers use the
integrated circuits. Its memory
capacity was 32,000to 4 million characters. Its internal operating speed was
nano seconds (10-9s). Its external speed was up to 10 crores
instruction per second.
Fourth
Generation (1975- 1989)
Fourth generation computers are
based on large scale integration or very large scale integration circuits.
Development of microprocessor also
happened in this generation. Its memory capacity is up to 51,200 to 32 million
characters. Its internal operating speed is pico seconds (10-12s)
and above. Its external speed is up to 100 millions per second.
Fifth
Generation (1989-present time)
Very Large Scale Integration technology became Ultra
Large Scale Integration
technology in fifth generation resulting in production of microprocessor chips
having 10 million electronic components.
On the basis of data, computers
are basically classified into three types:
1.
Digital Computer
A digital
computer operates directly on decimal digits that represent either discreet
data or symbols. It takes input & gives output in the form of numbers,
letters & special characters represented by holes in punched card,
magnetized area on tapes, printing on paper & so on. It is generally used
for business & scientific data processing.
2.
Analog computer
An analog
computer measures continuous electrical or physical magnitude like voltage,
pressure, shaft rotation etc. They are process control devices. The output from
the system may be in the form of a graph produced by a plotting pen or a trace
on a cathode ray tube. Its output signals can be used directly to control the
operation of some other machine for process. They can perform very complex
arithmetical functions at high speed while the actual process is in operation.
These computers have many applications in the scientific and industrial field.
3.
Hybrid computer
A
computer that combines the most desirable features of both digital and analog
is known as hybrid computer. They are suited for the situation where digital
processing of data is collected in analog form is desirable. Its processing
speed is faster than digital computer and accuracy is greater than analog
computer.
On the basis of capacity, price,
performance criteria, computer can be classified into four types:
1.
Mainframe computer
Mainframe
computers are general purpose computers capable of handling all kinds of
problems. It can accept & transfer data from I/O devices at the rate of
millions of bytes per second. It can support large number of terminals. They
have large online secondary storage capacity and can support a number and
variety of peripheral devices like magnetic tapes, drivers. They routinely have
high speed cache memories which enable them to process applications faster than
mini & micro computers.
2.
Super computer
Super
computers are big general purpose computers capable of executing more than ten
thousand instructions per second. It has the storage capacity of millions of
bytes per chip. The high speed in these computers is due to use of a number of
micro processor working in parallel and high storage densities are obtained by
using magnetic bubble memories and charged coupled devices, so reducing the
cost of storage.
3.
Mini computer
Mini
computers are smaller versions of the mainframe. Generally they offer the same
computing power as mainframe. The most important advantage of a mini computer
over the main frame is that it is cheaper in cost, smaller in size & very
reliable. The main use of these systems is in education, in local government
etc.
4.
Micro computer
The micro computers are built around micro
processor chips. It is a silicon wafer about 5mm square & 0.1mm thick with
layer of etched & printed circuits. It contains all the elements require to
process binary in coded data. It is possible to pack a complete micro computer
in a single chip but usually several chips are used. A typical micro computer
has a key board for input & uses floppy drives, CDs, or DVDs to inter data
and programs to receive outputs.
