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
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, Germany , broad out ENIAC. It was the first electronic calculator. In 1947, the
scientists of University of Pennsylvania, USA , broad out EDSAC. It was the first electronic
computer in the world. In 1951, Sperry Rand Corporation of Cambridge University,
UK introduced the first commercial
computer to the world & named it Universal
Automatic Computer (UNIVAC 1) USA
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 computerThe 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.