Types of Computer.The computer can be categorized:1) On the basis of Operation (or Work)

i) Analog Computerii) Digital Computeriii) Hybrid Computer

2) On the basis of size.i) Super Computerii) Mainframe Computeriii) Mini Computeriv) MicroComputer

a) Personal Computer.b) Workstation.c) Portable Computer (e.g. Laptops, Palmtops, Notebooks)

3) On the basis of brandi) IBM PC (International Business Machine Personal Computer)ii) IBM Compatibleiii) Apple/Macintosh

4) On the basis of modeli) XT (Extended Technology)_ii) AT (Advanced Technology)iii) PS/2 (Personal System-2)

On the basis of Operation (or Work)i) Analog Computer In this type of Computers, the information is represented by the magnitude of continuously varying signals. For e.g., numbers from 0 to 50 may be represented on a scale of 0 to 5 volts, so that 3.5 volts may represents the number 35. Thermometer measures temperature based on analog principle, it measures not by doing any calculations, but by comparing the relative expansion of mercury. Thus it measures physical values such as temperature or pressure that fall along a continuous scale or variance in temperature or pressure. Some example of analog devices is Service station gasoline pump, Speedometer in cars, motor cycles etc. Finally, we say a change measurement device with reference to other is called analog computer. Seismograph is an example of analog computer.

ii) Digital Computers: Digital Computers operate by counting discrete quantified data represented by electronic pulses. These electronic pulses are either "ON" or "OFF". An example of digital signal is

the electronic signal, which operates the oil pressure warning light in a car. The light glows and informs the driver only when the oil pressure is below a certain level. Digital Computers are used in number of applications. They are mainly used in data processing, word processing, documentation, graphical representation etc. The important features of digital computer are:

a) The things that can be done on analog computers can also be done on digital computer, however the reverse is not true.

b) Digital Computers may be used and understood without much mathematical background unlike in the case of analog computer.

c) The digital computers are accurate and are extensively used in many areas of applications.

d) The flexibility offered by digital computers is very high. iii) Hybrid ComputerThey are special purpose computer and design of which is formed by combining the design features of analog and digital computers. Hybrid computer can transfer data from analog to digital and vice versa. They are used in special application fields, like big industries, scientific research, airplane etc. Jetplanes are facilitated with hybrid computer and they can fly day and night towards the direction of destination assigned. The Computer gives information about humidity, air pressure, temperature, weight, speed etc. Before take off and in the air, the computer gives information about each component of plane.

On the basis of Sizei) Super Computers:

They belong to the most powerful class of computer. They are the fastest calculating machine ever invented. Super Computer can cost over $50 million each, so most super

computers are used by government agencies. These machines are for application requiring large programs and huge amount of data that must be processed quickly. Examples are weather forecasting, weapons research, animation, and large -scale simulation. Super Computer Y-MP/C90 made by Cray Research Inc. can perform as many as 2.1 billion mathematical calculations per second. More powerful Super Computer consists of thousands of integrated microprocessors. One massively parallel processing computer built by Intel Corporation is capable of performing 8.6 billion mathematical calculations per seconds. E.g. cray-1, ETA10, Y-MP/C90 etc.

ii)Mainframe: The mainframe computer is a large, fast multi-user computer system, designed to

manage very large amount of data and very complex computing task. Mainframes are usually installed in large corporation, Universities, or military installation, and can support hundreds, even thousands of users. They can be used for any types of application area because of their higher memory capacity. The space required for the installation of these computers is about 100 sq. feet because of its peripheral device connected to it are also very large viz. central processing unit, 4 to 8 tape

units,4 to 6 hard disk unit, many display unit and so on. Some examples of mainframe are IBM360, IBM370, IBM1401,ICL 2950/10.

iii)Minicomputer: They were introduced in 60's and are smaller than mainframe. They are medium

sized computer system capable of managing over 100 users simultaneously. They are suitable for use in small company or single corporation or government department. They support a variety of peripheral devices, software packages and languages. Examples are PDP11/45, VAX RANGE, Neck, Data General etc.

iv) Microcomputer: They are based on a single chip processor. The development of large-scale Integration (LSI) technology in the early 1970,s gave birth to microcomputers. They are small in size, low price, uses BASIC, FORTRAN, PASCAL,C/C++ etc languages. They support floppy disk, hard disk or magnetic tapes.

Types of Micro-computera) Personal Computer (PC): They are portable machine that is they can be carried easily

from place to place. Personal Computer is specially designed for use by one person at a time equipped with its own Central Processing Unit, memory, operating system, keyboard, and monitor, hard & floppy disk as well as peripheral when needed. This machine can run comparatively easy to use application software such as the word processor, spreadsheets etc. e.g. Acer, Compaq etc.

b) Workstations: They are expensive, powerful machine used by scientists, engineers, and other professionals who process a lot of data. Unlike PC, Workstations use sophisticated display screen featuring high-resolution color graphics and operating systems such as Unix that permitted multitasking. Workstations also use powerful networking links to other computers. The most significant distinguishable factor is powerful processor relatively to Personal Computer (PC). Examples are Sun, Apollo, NeXT etc. However, these days Personal as powerful as workstation are available.

c) Portable Computers: These Days Computer are becoming smaller as well as powerful. Laptops, Notebooks etc are examples of portable computers.Laptops may be either Ac-powered, battery powered or both. Laptop has a size smaller than that of a briefcase. They can be taken from one place to another on hand.Notebook is still smaller in size than Laptops. These Computer fit easily into any briefcase.