There are five generation of computer, these are:

(1) First Generations of Computers (1942-1959)

The beginning of commercial computer age is from UNIVAC (Universal Automatic Computer). The first generation computers were used during 1942-1959. They were based on vacuum tubes. Examples of first generation computers are ENIVAC and UNIVAC-1.

Advantage:

• Vacuum tubes were the only electronic component available during those days.

• Vacuum tube technology made possible to make electronic digital computers.

• These computers could calculate data in millisecond.

Disadvantages:

• The computers were very large in size.

• They consumed a large amount of energy.

• Non-Portable.

• Limited commercial use.

• Very slow speed.

• Used machine language only.

• Used magnetic drums which provide very less data storage.
  
  

(2) Second Generation Computers (1959-1965)

The second generation computers used transistors. The size of the computers was decreased by replacing  vacuum tubes with transistors. The examples of second generation computers are IBM 7094 series, IBM 1400 series and CDC 1604 etc.

Advantage:

• Smaller in size as compared to the first generation computers.

• Used less energy and were not heated.

• Better speed and could calculate data in microseconds.

• Used faster peripherals like tape drives, magnetic disks, printer etc.

• Used assembly language instead of Machine language.

Disadvantages:

• Cooling system was required

• Constant maintenance required

• Only used for specific purposes

• Costly and not versatile

(3) Third Generation Computers (1965-1975)

The Third generation computers used the integrated circuits (IC). The first IC was invented and used in 1961. The size of an IC is about ¼ square inch. A single IC chip may contain thousands of transistors. The computer became smaller in size, faster, more reliable and less expensive. The example of third generation computers are IBM 370, IBM System/360, UNIVAC 1108 and UNIVAC AC 9000 etc.

Advantages:

• Smaller in size as compared to previous generations.

• More reliable.

• Used less energy.

• Better speed and could calculate data in nanoseconds.

Disadvantages:

• Air conditioning was required.

• Highly sophisticated technology required for the manufacturing of IC chips.

(4) Fourth Generation Computers (1975-1988)

The fourth generation computers started with the invention of Microprocessor. The Microprocessor contains thousands of ICs. The LSI (Large Scale Integration) circuit and VLSI (Very Large Scale Integration) circuit was designed. It greatly reduced the size of computer. The size of modern Microprocessor is usually one square inch. It can contain millions of electronic circuits. The examples of fourth generation computers are Apple Macintosh and IBM PC.

Advantages:

• More powerful and reliable than previous generations.

• Small in size.

• Fast processing power with less power consumption.

• Fan for heat discharging and thus to keep cold.

• Cheapest among all generation.

• All types of high level languages can be used in this type of computers.

Disadvantages:

• The latest technology is required for manufacturing of Microprocessors.
  
  

(5) Fifth Generation Computers (1988 to Present)

Scientists are working hard on the fifth generation computers with quite a few breakthroughs. It is based on the technique of Artificial Intelligence (AI). Computers can understood spoken words and initiate human reasoning. IBM Watson computer is one example that outsmarts Harvard University Students.

Computer Generations-