# Chapter CLASSIFICATION OF COMPUTERS BY TYPES

### CLASSIFICATION OF COMPUTERS BY TYPES

The computer have been classified into three categories according to their types.
1. Analog Computers
2. Digital Computers
3. Hybrid Computers

#### ANALOG COMPUTERS

‘Analog’ is basically a Greek Word, which means ‘similar’.Analog Computer works on the principle of measurement.So,analog computers are based on the similarities between any two quantities.These two quantities are measured by electrical quantities.
This machine has a very limited memory.Also,it can perform only a limited types of calculations.Although analog computer performs calculations at a very high speed,yet the accuracy of this machine is very low.

#### DIGITAL COMPUTERS

Digital Computers operate on quantities represented by digits.These digits are in the form of binary digits, i.e. 0 and 1.All the operations of Digital Computer are carried by using these two digits at a very high speed.
In digital computer, both numeric and non-numeric information is represented as string of digits.The information is given to the computer in the form of discrete electrical signals.Presonal Computer is an example of Digital Computer.This computer works on the Principle of Counting rather than measuring.

#### HYBRID COMPUTERS

Hybrid computers is the combination of both Analog Computers and Digital Computers.These computers are special purpose instruments which are mostly used in the Hospitals like E.C.G., CATSCAN etc.

#### GENERATIONS OF THE COMPUTERS

Here, the term “Generatiion” refers to major developments in the computers.Each phase of development has its unique features which separates it from the previous invented computers.The generations are mainly divided into five phases.

##### THE FIRST GENERATION COMPUTERS(1945-59)

In the first generation computers (ENIAC,EDVAC,UNIAC etc ), vaccum tubes,were used.To work on these computers it is necessary to learn machine language for giving instructions.
ENIAC was the world’s first successful computer.It was developed in 1946 by J.W. Mauchly and J.P. Echert.
The power needed by ENIAC was large enough and it was huge machine.While working, it generate more heat. It contained 1800 vaccum tubes . A water cooling system was also needed.

##### THE SECOND GENERATION COMPUTERS(1959-65)

In 1947 three scientists H.W. Brattain, J.Bardeen and W.Shockley developed the transistor at Bell Laboratories.The transistors performed the same functions as the vaccum tube.The transistor was smaller and less expensive.It generated almost very negligible heat and requires less power.Computers in which transistor were used called second generation computers. Storage capacity of computer increased.
The development of low level language i.e. assembly language and high level language i.i. FORTRAN started.The example of second generation computers are IBM-700, IBM 1401, IBM 1620 and UNIVAC 1108.

##### THE THIRD GENERATION OF COMPUTERS (1965-70)

The third generation computers replaced transistors with integrated circuits.These computers had much higher speeds , large storage capacity, and cheap in price.
Instead of having one transistor working separately,several transsitors were integrated together with other components and sealed in a small package.This package is called Integrated Circuit (I.C) or the chip.IBM 360, ICL 2900, NCR 395 are the examples of third generation computers.

##### THE FOURTH GENERATION COMPUTERS (1970-85)

This period was a period of tremendous development in the field of computer technlogy. In these computers, very large scale Integrated (VLSI) technology are used.VSLI technology, microprocessor chip contains an entire Central Processing Unit (C.P.U) on a single silicon chip.The processing speed and memory capacity increased by ten and four times respectively.Some fourth genration computers are IBM 4341, DEC 10, APPLE II, Microprocessor,Pentium, Power PC , Star 1000 etc.

##### THE FIFTH GENERATION COMPUTERS (1985-present)

With the advancement in Science and Technology, the scientists and Researchers are working hard on fifth generation of computers.The fifth generation computers combine hardware and software to produce human intelligence.In future we may see a machine that can think like human beings and may be capable to take decisions.