EISA BUS

10/25/97

Extended Industry Standard Architecture (EISA) Bus: The EISA Bus was developed in 1988 by a consortium of computer suppliers led by Compaq Computer. It was developed as a response to IBM's MicroChannel Architecture Bus. The EISA bus is fully compatible with the AT bus with extra signals cleverly placed on Pins located above and between the existing AT bus pins.

EISA was used primarily for high end PCs such as graphics workstations and servers. It has largely been replaced by VLB and PCI, but EISA cards are still available from a few vendors.

EISA resembles MCA in some respects. It is a 32 bit bus clocked at 8.33MHz. It requires a special BIOS and usually special set up software and drivers. The EISA bus supports bus mastering and burst mode data transfers. By convention, EISA cards use port addresses above 400. Since many ISA bus cards do not decode the high order bits, EISA cards may alias to addresses that conflict with ISA cards. EISA includes slot as well as board addressing allowing board identifications to be read by slot. EISA also supports optional level triggered Interrupts.

The maximum theoretical data rate for the EISA bus is 33 MBytes per second. In practice, EISA surely can not come close to that rate, but it may come closer to its maximum than ISA or AT because of its burst capability.