The Peripheral Component Interconnect standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard (a so-called local bus). These devices can take the form of:
- integrated circuits fitted on the motherboard itself (called planar devices in the PCI specification); or
- expansion cards that fit in sockets.
PCI occurs commonly in
PCs, where it has displaced
ISA as the standard bus, but it also appears in other computer types. Unlike ISA buses, the PCI bus enables dynamic configuration of a peripheral device. At boot up time the PCI card's
BIOS and the system BIOS interact and negotiate the resources that the PCI card requests. This enables allocation of IRQs and port addresses through a dynamic process, unlike the ISA bus case which required manual configuration of IRQs using external jumpers. Apart from this, the PCI bus provides a detailed description of all the connected PCI devices through the
PCI Configuration Space.
The PCI specification covers the physical size of the bus (including wire spacing), electrical characteristics, bus timing and protocols. The PCI Special Interest Group (PCISIG) sells copies of the specification at http://www.pcisig.com/.
Basic PCI Bus Specifications
- 33MHz clock with synchronous transfers
- peak transfer rate of 133MB per second
- 32-bit bus width
- 32-bit address space (4G bytes)
- 3.3 volt or 5 volt signalling
- reflected-wave switching
Basic PCI Variants
- PCI 2.2, allows for 64-bit bus widths and/or 66MHz signalling (peak transfer 533 MB/s)
- PCI-X, 64-bit version of 2.2 that increases the data rate to 133MHz (peak transfer 1066 MB/s)
- PCI-X 266 (or PCI-X DDR), "double-pumped" PCI-X for 266MHz rates (peak transfer 2133 MB/s)
- Mini PCI
- Compact PCI, uses Eurocard-sized modules using PCI as a backplane
Other PCI Variants
- PCI-Express (or 3GIO), a serial bus using PCI signalling and programming concepts
See also:
