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Extended Industry Standard Architecture (EISA) Bus

EISA stands for Extended Industry Standard Architecture. Unlike ISA, here the name is not indicative of reality, for the EISA bus never became widely used and cannot by any stretch of the imagination be considered an industry standard. EISA began as Compaq's answer to IBM's MCA bus, and followed a similar path of development--with very similar results.

Compaq avoided the two key mistakes that IBM made when they developed EISA. First, they made it compatible with the ISA bus. Second, they opened the design to all manufacturers instead of keeping it proprietary, by forming the non-profit EISA committee to manage the design of the standard. EISA was similar to MCA both in terms of technology and market acceptance: it had significant technical advantages over ISA, and it never caught on with the PC-buying public.

Some of the key features of the EISA bus:

• ISA Compatibility: ISA cards will work in EISA slots.
• 32 Bit Bus Width: Like MCA, the bus was expanded to 32 bits.
• Bus Mastering: The EISA bus supports bus mastering adapters for greater efficiency, including proper bus arbitration.
• Plug and Play: EISA automatically configures adapter cards, similar to the Plug and Play standards of modern systems.

EISA-based systems have today been mostly relegated to a specialty role; they are sometimes found in network fileservers. The EISA bus is virtually non-existent on desktop systems for several reasons. First, EISA-based systems tend to be much more expensive than other types of systems. Second, there are few EISA-based cards available. Finally, the performance of this bus is quite low compared to the popular local buses like the VESA Local Bus and PCI. EISA is not totally dead as a platform the way MCA is, but it is pretty close.

Next: VESA Local Bus (VLB)

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