Though computers do not have a very long history behind them, but they have very rapid evolutionary changing phases within a very short span. Such evolution puts tremendous impact on our socio-economic life that brings a total revolution in itself. Each time evolved computers are coming out with better advantages and we call these "Generation of Computers."
So far we have four generations i.e. first, second, third and fourth generation of computers depending on their design, speed, size and performance. The fifth ones are on progress. These generations of computers plan to give highest priority to make the computers easy to handle and natural to use.
First Generation Computers (1946-1959) -Vacuum Tubes
For calculation of ballistics, Eckert and Mach built the first electromechanical computer, the Electronic Numerator Integrator Analysis and Computer (ENIAC) in Feb, 1946. These computers used vacuum tubes and were bulky. Each ENIAC had 18.000 vacuum tubes, about 70,000 resistors, 10,000 capacitors and 6,000 switches. They had limited memory and punched card orientations for input and output of data and used low level programming language and had primitive operative systems.
ENIAC was followed by EDVAC (Electronic Discrete Variable Automation Computer), EDSAC and IBM 650 (International Business Machines).
Second Generation Computers (1959-1964) – Transistor
Computers belonging to this group used transistors which were made of semiconductors. Hence they were compact and smaller in size. They required less electricity than a valve, had high speed (about 106 operations/second) and reliability, larger memory and accepted high level languages like COBOL, FORTAN etc. They had magnetic tap orientations and were designed for batch oriented applications, updating, inventory and airline payroll processing. The best examples are IBM 1401. Honey well 200, CDC 1604, etc.
Third Generation Computers (1965-1970) - Integrated Circuit
The arrival of the Integrated Circuit or 1C brought along with it, the improvement on the second generation computers. The ICs' were hundreds of times smaller than the transistor circuits and were cheaper and more reliable than the transistors. Hence all the computers using ICs' were third generation computers. Their sizes were small and they had high processing speed (108 operations per second), easy maintenance, faster and versatile input/output devices, large storage capacity, greater use of high level programme languages, application of soft wares and packages. These were mostly general purpose computers, real-time applications with remote processing, reservations, marketing, forecasting, credit card bills etc. IBM system 360, CDC 6000/7000 series, Burroughs B 6500, NCR 395, ICL 1900/2900 series are some of the important examples.
In 1972, Microcomputers came into the market, where the entire central processing unit (CPU) was built on a single chip i.e., Microprocessor. So by end of 1972, we had calculators, control equipment computers etc. The day the microprocessors invaded into our lives, they put a major impact on our day-to-day life. Fourth Generation Computers (1971-?) -Large Scale Integration
These computers use very large scale integrated (VLSI) circuits. They possess much larger computing power, extreme large memories and greater versatility of input/output (I/O) devices. The emergences of micro computers bring out the story of the evolution of computers of the present day. A microprocessor of few grams weight—e.g. a thin "2 x 1" silicon chip can store 512 x 1024 bits (Bit = binary digit) of Os and Is. IBM 3081, ISM 370, CYBER, CRAY, FLOSOLVER. PARAM super computers etc. are the examples of some important ones. Fifth Generation Computers
Tremendous revolution of computers has taken place during the later part of the 20th century. Hence now it is called the "Age of computers". After fourth generation, fifth generation computers are already developed. The main aim of this computer is to use them to areas where it has not been used earlier. These are called "Artificial Intelligence."