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| ISA 8 and 16Bit |
ISA stands for Industry Standard Architecture.
The ISA bus was developed by a team led by Mark Dean at IBM as part of the
IBM PC project in 1981. It originated as an 8-bit system and was extended in
1983 for the XT system architecture. The newer 16-bit standard, the IBM AT
bus, was introduced in 1984.
Designed to connect peripheral cards to the motherboard, ISA allows for bus
mastering although only the first 16 MB of main memory are available for
direct access. The 8-bit bus ran at 4.77 MHz (the clock speed of the IBM PC
and IBM PC/XT's 8088 CPU), while the 16-bit bus operated at 6 or 8 MHz
(because the 80286 CPUs in IBM PC/AT computers ran at 6 MHz in early models
and 8 MHz in later models.) IBM RT/PC also used the 16-bit bus. |
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