Extended Industry Standard Architecture
The Extended Industry Standard Architecture (EISA), «extended industry standard architecture», is an architecture bus for IBM PC compatible computers. Announced in late 1988, it was developed by the so-called "Group of Nine" (AST, Compaq, Epson, Hewlett-Packard, NEC Corporation, Olivetti, Tandy, Wyse, and Zenith Data Systems), vendors of clone computers, in response to IBM's use of the proprietary MicroChannel bus architecture (MCA) in the IBM Personal System/2 series. It saw limited use in 386 and 486 personal computers until the mid-1990s, when it was replaced by local buses such as the VESA bus and PCI.
Technical characteristics
EISA extends the ISA bus architecture to 32-bit and allows more than one CPU to share the bus. The bus mastering support is also enhanced to allow access to up to 4 GB of memory. Unlike MCA, EISA is backward compatible with ISA, so it can accept older ISA cards for XT or AT and clones, the connections and slots being an extension of the ISA bus.
Despite being somewhat inferior to MCA, the EISA standard was highly favored by vendors due to the proprietary nature of MCA, and even IBM made some machines that supported it. But at the time when there was a strong demand for a bus with these speeds and features, the VESA bus and later the PCI bus filled this niche and the EISA disappeared.
EISA introduces the following enhancements over ISA:
- 32-bit memory addresses for CPU, DMA, and bus master devices.
- Synchronous transmission protocol for high-speed transfers.
- Automatic translation of bus cycles between EISA and ISA teachers and slaves.
- Support for intelligent master peripheral controllers.
- 33 MB/s transfer speed for master buses and DMA devices.
- Interruptions (IRQshared.
- Automatic system configuration and expansion cards.