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1.3. Different Types of Microcomputers

Today most of the microcomputers are IBM compatible. The microcomputers compatible with the line of IBM personal computers are known as IBM compatible computers.

Compatibility here means that, components (hardware and software) of one ‘IBM computer’ is normally installable in another ‘IBM compatible computer’ and vice-versa. All IBM compatible computers have same line of microprocessor, input-output device, software etc. So it is possible to use one component of a computer in a compatible of that computer.

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Different series of IBM compatible computers exist. They are:
i)  IBM PC
ii) IBM PC/AT
iii) IBM PC/XT
iv) IBM PS/2.

1.3.1. IBM PC
IBM PC was introduced in 1981. It has following characteristics:
i) Intel 8088 processor
ii) 16 KB RAM expandable up to 64 KB
iii) Monochrome video adapter, incapable of displaying bit-mapped graphics
iv) Floppy disk drive with 160 KB storage capability
v) No hard disk.

‘PC’ is the name of a compatible series of microcomputers. But this name ‘PC’ is also used to refer any microcomputer, where PC means personal computer. In this book where we used the term ‘PC’, it means any microcomputer except in this section.

1.3.2. IBM PC/XT

IBM PC/XT was introduced in 1983. It has following characteristics:

i) Intel 8088 processor

ii) RAM expandable up to 640 KB

iii) Supports hard disk.

1.3.3. IBM PC/AT

IBM PC/AT was introduced in 1984. It has following characteristics:

i) Intel 80286 processor

ii) It is approximately 75% faster than PC/XT

iii) AT bus standard was used in many clones.

‘Bus standard’ means the industry standard of connection point and connection organization of different devices connected with the motherboard.

‘Clone’ means a copy of the original one. In computer literature, it means compatibility. For example, ‘AT clone’ means a computer compatible to the IBM PC/AT series.

1.3.4. IBM PS/2

It was introduced in 1987. Different types of Intel processors are used here. It uses MCA (Micro Channel Architecture) bus standard.