12 Facts About ISA bus

The ISA term was coined as a retronym by competing PC-clone manufacturers in the late 1980s or early 1990s as a reaction to IBM attempts to replace the AT-bus with its new and incompatible Micro Channel architecture.

Original PC ISA bus was developed by a team led by Mark Dean at IBM as part of the IBM PC project in 1981.

In 1988, the 32-bit EISA bus standard was proposed by the "Gang of Nine" group of PC-compatible manufacturers that included Compaq.

The ISA bus was therefore synchronous with the CPU clock, until sophisticated buffering methods were implemented by chipsets to interface ISA to much faster CPUs.

MCA overcame many of the limitations then apparent in ISA bus but was an effort by IBM to regain control of the PC architecture and the PC market.

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MCA was far more advanced than ISA bus and had many features that would later appear in PCI.

Users of ISA bus-based machines had to know special information about the hardware they were adding to the system.

Microsoft's PC 99 specification recommended that ISA bus slots be removed entirely, though the system architecture still required ISA bus to be present in some vestigial way internally to handle the floppy drive, serial ports, etc.

ISA bus slots remained for a few more years, and towards the turn of the century it was common to see systems with an Accelerated Graphics Port sitting near the central processing unit, an array of PCI slots, and one or two ISA bus slots near the end.

ATA has since been separated from the ISA bus and connected directly to the local bus, usually by integration into the chipset, for much higher clock rates and data throughput than ISA could support.

The XT ISA bus architecture uses a single Intel 8259 PIC, giving eight vectorized and prioritized interrupt lines.

However, with the popularity of the AT-architecture and the 16-bit ISA bus, manufacturers introduced specialized 98-pin connectors that integrated the two sockets into one unit.