The PCI bus supports the functions found on a processor bus but in a standardized format that is independent of any particular processor's native bus.
Devices connected to the PCI bus appear to a bus master to be connected directly to its own bus and are assigned addresses in the processor's address space.
It is a parallel bus, synchronous to a single bus clock.
Attached devices can take either the form of an integrated circuit fitted onto the motherboard itself (called a planar device in the PCI specification) or an expansion card that fits into a slot.
The PCI Local Bus was first implemented in IBM PC compatibles, where it displaced the combination of several slow ISA slots and one fast VESA Local Bus slot as the bus configuration.
It has subsequently been adopted for other computer types.
Typical PCI cards used in PCs include: network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards and disk controllers.
PCI video cards replaced ISA and VESA cards until growing bandwidth requirements outgrew the capabilities of PCI.
The preferred interface for video cards then became AGP, itself a superset of conventional PCI, before giving way to PCI Express.
The first version of conventional PCI found in consumer desktop computers was a 32-bit bus using a 33 MHz bus clock and 5 V signalling, although the PCI 1.0 standard provided for a 64-bit variant as well. Version 2.0 of the PCI standard introduced 3.3 V slots, physically distinguished by a flipped physical connector to prevent accidental insertion of 5 V cards.
Universal cards, which can operate on either voltage, have two notches.
Version 2.1 of the PCI standard introduced optional 66 MHz operation.