EISA – Extended Industry Standard Architecture

Extended Industry Standard Architecture (in practice almost always shortened to EISA and frequently pronounced “eee-suh“) that extends the ISA standard to a 32-bit interface. It was developed in part as an open alternative to the proprietary “Micro Channel Architecture (MCA)” that IBM introduced in its PS/2 computers. It is a bus standard for IBM compatible computers. It was announced in late 1988 by PC clone vendors as a counter to IBM’s use of its proprietary Micro channel Architecture (MCA) in its PS/2 series.

EISA is the term used to describe the expansion slots and related circuitry (the expansion bus) found in some higher-priced PCs. If you see an ad for an EISA computer, it’s talking about a PC with EISA slots.

EISA was developed by a group of PC manufacturers to compete with IBM’S Micro Channel expansion slots, the kind found in most IBMPS/2 computers. Like the Micro Channel slots, EISA slots can transfer 32 bits at a time at high speed, compared with 8 or 16 bits at relatively slow speeds for the standard slots in a regular pc. But EISA slots have the advantage of accepting standard PC add-in boards, which are by far the most common type you can buy, and which won’t fit in the Micro Channel slots.

EISA extends the AT bus, which the PC clone Vendors retroactively renamed to the ISA bus to avoid infringing IBM’s trademark on its PC/AT computer, to 32 bits and allows more than one CPU to share the bus. The bus mastering support is also enhanced to provide access to 4 GB of memory. Unlike MCA, EISA can accept older XT and ISA boards – the lines and slots for EISA are a superset of ISA.

EISA was much favored by manufacturers due to the proprietary nature of MCA, and even IBM produced some machines supporting it. It was somewhat expensive to implement, so it never became particularly popular in desktop PCs. However, it was reasonably successful in the server market, as it was better suited to bandwidth-intensive tasks. Most EISA cards produced were either SCSI or network cards. EISA was also available on some non-IBM compatible machines such as the Alpha Server, HP 9000-D, SGI Indigo2 and MIPS Magnum.