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Acronym for Extended Industry Standard Architecture, a bus architecture designed for PCs using an Intel 80386, 80486, or Pentium microprocessor. EISA buses are 32 bits wide and support multiprocessing.

The EISA bus was designed by nine IBM competitors (sometimes called the Gang of Nine): AST Research, Compaq Computer, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems. They designed the architecture to compete with IBM's own high-speed bus architecture called the Micro Channel architecture (MCA).

The principal difference between EISA and MCA is that EISA is backward compatible with the ISA bus (also called the AT bus), while MCA is not. This means that computers with an EISA bus can use new EISA expansion cards as well as old AT expansion cards. Computers with an MCA bus can use only MCA expansion cards.

EISA and MCA are not compatible with each other. This means that the type of bus in your computer determines which expansion cards you can install.

Neither EISA nor MCA has been very successful. Instead, a new technology called local bus (PCI) is being used in combination with the old ISA bus.

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