Classification of computer
We can define Computer Classification  into four categories based on the Principle of Operation, Throughput, Number of Users, and Technology Evolution.

Principle of operation

Computer can be classified into three different types on the basis of the principle of operation. They are analog, digital, and hybrid computer.

1-Analog computer process the data, represented in the form of continuous signals such as voltage, temperature, pressure, etc. They are more accurate, but slow in processing speed than the digital computers.
A very simple example of analog computer is a car speedometer.

2-Digital computer essentially is a machine that works on discrete digits or numbers i.e., 0 and 1 (binary digits). Personal computers are the example of digital computer.

3-Hybrid computer combine the best characteristics of analog and digital computer. They provide higher precision than analog computers with greater control and speed than digital computer.

Throughput refers to the measure of processing capacity that a computer can deliver in a given period of time. Computers can be classified into four categories based on throughput. They are microcomputer, minicomputers, mainframes, and supercomputer.

I – Micro computer: Have CPU on a single chip with limited processing power and storage capacity. Micro computer are based on micro processor chips. They are commonly known as personal computer and they are 64/32 bit machines. e.g. PCs, Palmtop, Laptop,  IBM- PCs etc
ii –Minicomputer: Mini computer is a mini version of of mainframe computer and is smaller and cheaper. Mini computer are 16-bit machines. A 16-bit mini computer has efficient storage and handling of text, in comparison to lower bit machines. Example V AX-I I, PDP-II, DEC V AX 8800.

iii- Mainframe: Are large general purpose computer capable of handling scientific and commercial applications. They have large processing power and storage capacity which supports multiple terminals. These computer generally 32 bit or on the higher side. They have very large disks to store several Giga Bytes of a data and transfer data from disks to main memory at several  hundreds Mbps. E.g. Medha, Sperry, DEC , ICl, IBM 3033/3090.

iv- Supercomputer: Are large general  purpose computers capable of executing more than 10,000 Million Instruction Per Second(MIPS) and have storage capacity of millions of bytes. They have multiple CPUs working in parallel under the control of Microkernel  operating system and Multithreaded programming environment. E.g CRAY  Y-2, ETA, HITACHI and PARAM 9000.

If we say on the basis of purpose: Computer is basically divided into two categories.

a)General Purpose Computer: Computer that follow instruction for general requirement such as sales analysis, financial accounting, invoicing, management information etc.

b)Special Purpose Computer: Computer that are designed from scratch to perform special task like scientific application and research, weather  forcasting, space applications, medical diagnosis, etc.

Number of users:
Computer can be classified into two types based on the number of users operating simultaneously. They are single user and multi user computers

i – SINGLE USER COMPUTERS: Have less processing power and only one user can operate at a time with single task execution. The single user operating system such as Disk Operating System(DOS) is used on such as system Eg. Microcomputers.

ii – MULTI -USER COMPUTERS: Are large in processing power and storage capacity. It supports multiple users simultaneously and creates an illusion as if each user has a dedicated computer system. The multi user operating system such as UNIX and VAX can be used on such system.

Technology Evolution:
Computer can be classified based on technology evolution into zero, first, second, third, fourth, and fifth generation. The generation of computer with their associated development is shown in table:



Generation Year Example


Computer Hardware Computer Software Computer Performance
Zero Pre 1947 Abacus, Difference Engine, Analytical Counter Wheels with Mechanical Components ————– Numerical Operations at slow speed
First 1946-1956 Enivac, Udvac, Univac IBM 650 Vacuum Tubes, Magnetic Drums, CRT Screens Stored Programs Machine Codes 2 KB Memory 10 Kilo Instruction Per Second (KIPS)
Second 1957-1963 IBM 7094, CDC6600 Honeywell 400 Burroughts 5000 Transistor, Magnetic Code Memory HLL, FORTRAN COBOL ALGOL 32 KB Memory 5 MIPS
Third 1964-1981 IBM 360/370 Honeywell 2000, Cray-I CYBER 205 ICs, Semiconductor Memory, Magnetic Disk Pascal, C, Time Sharing System 2 MB Memory 5 MIPS
Fourth 1982 Cray –XMP IBM 305 Distributed Computing System, VLSI, Bubble Memory Optical Disk OOP Languages, C++ 8 MB memory 30 MIPS
Fifth 1990 PARAM 9000, C-DAC, CRAY-II C Parallel Architecture, Optical and Neura Computing Multi threaded Parallel programming Models 1 Giga to 1 Tera Instruction pre second.
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