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The PCI local bus standard defines a method for connecting both ASIC chips and plug-in expansion cards to a computer's main memory and processing circuitry. Power Macintosh computers use the PCI bus or buses to communicate both with internal I/O chips and with plug-in expansion cards. This book discusses Apple's implementation of the PCI bus for expansion cards.
Apple's underlying policy is to support the PCI standard, as expressed in PCI Local Bus Specification, Revision 2.1, referred to here as the PCI specification. This standard specifies the logical, electrical, and mechanical interface for expansion cards, so that any card that conforms to it should be compatible with any computer that supports it. Hence expansion cards designed to be compliant with the PCI specification are generally hardware compatible with Power Macintosh computers and with other computers that comply with PCI, including computers that do not use Mac OS. The PCI specification is listed under Supplementary Documents.
Buses conforming to the PCI standard include the following main features:
A PCI bus is typically connected to the computer's processor and RAM system by an ASIC chip called a PCI bridge. Power Macintosh computers contain a proprietary bridge chip to connect their PCI buses to the PowerPC processor bus.