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Developments over the years have resulted in machines with greatly increased speeds, storage or memory, and computing power. These developments were so far-reaching and numerous that they are generally categorized by generations. Each generation is initiated by significant advances in computer hardware or computer software that run the machines.


The development of electronic computers can be divided into five (05)  generations depending upon the technologies used. The main five generations of computers are:
  1. First Generation (1942-1955 : Vacuum tube based)
  2. Second Generation (1955-1964 : Transistor based)
  3. Third Generation (1964-1975 : Integrated Circuit based)
  4. Fourth Generation (1975-Present : VLSI microprocessor based)
  5. Fifth Generation (Present & Beyond : ULSI microprocessor based)

Quick navigation: History of Computers

1. First Generation (1942-1955 : Vacuum tube based):

First generation computers utilized vacuum tubes in their circuitry and for the storage of data and instructions. The vacuum tube was bulky, caused tremendous heat problems, and was never a completely reliable device, it caused a great number of breakdowns and inefficient operations. Magnetic cores began to replace the vacuum tube as the principal memory device in the early machines. Small doughnut-shaped cores were strung on wires within the computer. Programs were written in machine language employing combinations of binary digits 0 and 1.

Features:
  • Vacuum tube technology
  • Supported machine language only
  • Unreliable
  • Generated lot of heat
  • Very costly
  • Slow input and output devices
  • Huge size
  • Need of A.C.
  • Consumed lot of electricity
  • Non-portable

Example: ENIAC, EDSAC, EDVAC, UNIVAC, IBM-701, IBM-650, Mark-II, Mark-III

Advantages:
  • 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:
  • They consumed a large amount of energy.
  • The computers were very large in size.
  • They were not very reliable.
  • They heated very soon due to thousands of vacuum tubes.
  • Air conditioning was required.
  • Constant maintenance was required.
  • Costly commercial production.
  • Limited commercial use.
  • Limited programming capabilities.
  • Non-portable.
  • Very slow speed.
  • Used machine language only.
  • Used magnetic drums which provide very less data storage.
  • Used punch cards for input.
  • Not versatile and very faulty.

2. Second Generation (1955-1964 : Transistor based)

The second generation of computer was marked by the use of transistors in Place of vacuum tube. L Invention of transistors at Bell t.abs by John Bardeen William Shockley and Walter Brattain Transistors had n number of advantages over the vacuum tube. As transistors were made from pieces of silicon , so they were more compact than vacuum tubes.

Features:
  • Transistors were used instead of vacuum tube
  • Processing speed in faster than first generations computer microsecond
  • Smaller in size (51 square feet) 
  • The input and output devices were faster

Example: IBM 1400, IBM 1600 IBM 1620, RCA 501, GE 200

Advantages:
  • Smaller in size as compared to the first generation computer
  • More reliable.
  • Less heat generated and less prone to hardware failures.
  • Better portability
  • Wider commercial use,
  • They were slightly-faster.

Disadvantages:
  • Air condition required.
  • Frequent maintenance required.
  • Commercial production was difficult and costly.

3. Third Generation (1964-1975 : Integrated Circuit based)

They were still more compacting faster and less expensive than previous generation along with the previous generation. This computer used "Integrated Circuit". These replacing the transistors, which was used in second-generation computer It uses integrated circuits (IC). It integrates large no of circuit's elements into surface of silicon chips these computers used IC for CPU computer. In the beginning they use magnetic core memory but later they used semi conductor memory. Semi conductor memory was LSI chip magnetic disk drums & tape was used as secondary memory. cache memory was also incorporated. Micro-programming, parallel programming, multi programming, multi user system (time sharing system) etc. were used. Multiprocessing too. The concept or virtual memory was also introduced.

Features:
  • They used integrated circuit chips in place of the transistors
  • Semi conductor memory devices were used 
  • The size was greatly reduced the speed of processing was high they were more accurate and reliable 
  • Larger scale integration and very large scale integration were also developed 
  • The mini computers were introduction in this generation
Example: IBM 360, IBM 370, PDP-8, PDP-II, GE 600

Advantages:
  • Smaller in size as compare to previous generation.
  • More reliable.
  • Lower heat generated
  • Computational time was reduced from micro second to nano second
  • Maintenance cost was low because hardware failure was rare
  • Portable
  • Used for commercial application
  • Less power required than previous of generation of computer
  • Commercial production was easier and inexpensive
  • They were totally generally purpose machine.

Disadvantages:
  • Air condition was required in many cases
  • Highly sophisticated technologies was required for the manufacturing of IC chip

4. Fourth Generation (1975-Present : VLSI microprocessor based)

Fourth generation use VLSI chips for both CPU and memory. CPU consists of one or more microprocessors. The latest microprocessors can contain one million transistors. Cache memory is provided on CPU chip.

Features:
  • They used microprocessor (VLSI) as their main switching element 
  • They are also called as micro computer or personal computers. 
  • Their size varies from desktop to laptop or palmtop 
  • They have very high speed of processing they are 100% accurate reliable diligent and versatile 
  • They have very large storage capacity

Example: IBM 3030, IBM 4341, IBM PC, HP 3000, PC 1211

Advantages:
  • Smaller in size because of high density of component in a small chip.
  • Very reliable
  • Heat generation very low
  • Less Powerful air conditioning
  • Faster computation
  • Minimum maintenance is required
  • In expensive among all generation
  • They were totally generally purpose machines

Disadvantages:
  • Highly sophisticated technology required for the manufacturing of 151 chip

5. Fifth Generation (Present & Beyond : ULSI microprocessor based)

These computers required genuine IQ that Is ability to reason logically and contain real knowledge. The structure will be parallel. They will be able to perform multiple tasks simultaneously. Data arid knowledge are processed they shall follow 'kips' than dips/lip.

Features:
  • They are the future computer which will use parallel processor or genetically engineered bio chips as their main switching element
  • They will have artificial intelligence and will be able to understand natural language.
  • They will have extremely high efficiency and reliability.

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