The Extended Industry Standard Architecture (EISA) is a bus standard of IBM PC-compatible computers. It was introduced by a consortium of PC clone vendors (known as the Gang of Nine) as an alternate option to IBM’s proprietary Micro Channel Architecture (MCA) of its PS/2 PC series. 

Compared to the ISA bus, EISA is extended to 32 bits and allows multiple CPUs to share the bus. The bus mastering support is also enhanced to enable access to 4 GB of memory. It can also accept older XT and ISA boards, compared to the MCA.

EISA was also more favored by manufacturers due to the proprietary nature of MCA; even IBM made machines that supported it. However, it was unpopular with most desktop PCs because of its cost. But, EISA was particularly successful in the server market since it was great at handling bandwidth-related tasks, like networking and disk access.



The EISA bus slot is a two-level staggered pin system, with the upper part corresponding to the ISA bus pin layout. Most additional features of the EISA are integrated at the bottom of the slot conductor, using thin traces inserted into the insulating gap of the ISA card edge connector. Also, the lower portion of the bus has five keying notches to prevent ISA cards with long notches from sliding down to the lower part of the slot.

Intel introduced its first EISA chipset—with code 82350—in September 1989. The company also launched a lower-cost variant, 82350DT, in 1991.

The world’s first EISA computer was the HP Vectra 486, announced in October 1989. Notable EISA computers that were introduced to the market were the SystemPro (1989) and the Compaq Deskpro 486 (1991). The SystemPro was the first PC-style network server built around EISA technology; it had features like multiprocessing, bus-mastering network cards, and hardware RAID.


The Gang of Nine

The Gang of Nine was the informal name given to the consortium—association of several companies with pooled resources—of personal computer (PC) manufacturing companies that collaboratively created the EISA bus. The known leader of the group was Compaq, an American information technology company.

Rival companies recognized Compaq’s leadership, with one company citing that: “when you have ten people sit down before a table to write a letter to the president, someone has to write the letter. Compaq is sitting down at the typewriter.” Its member companies were:

  • Compaq Computer Corporation
  • Seiko Epson Corporation
  • NEC Corporation
  • AST Research, Inc.
  • Hewlett-Packard Company
  • Tandy Corporation
  • Olivetti
  • Zenith Data Systems
  • Wyse Technology