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Home > Peripheral Component Interconnect

PCI expansion slots on a motherboard The Peripheral Component Interconnect standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. 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.

The PCI bus occurs commonly in PCs, where it has displaced ISA and VESA Local Bus as the standard expansion bus, but it also appears in many other computer types.

The PCI specification covers the physical size of the bus (including wire spacing), electrical characteristics, bus timing and protocols. The specification can be purchased from the PCI Special Interest Group (PCISIG).

1 History

Work on PCI began at Intel circa 1990. PCI 1.0, which was merely a component-level specification, released June 22, 1992. PCI 2.0, which was the first to establish standards for the connector and motherboard slot, was released on April 30, 1993.

PCI was immediatly put to use in high-end servers, replacing MCA and EISA as the server expansion bus of choice. In mainstream PCs, PCI was slower to replace VESA Local Bus (VLB), and did not gain significant market penetration until late 1994 in second-generation Pentium PCs. By 1996 VLB was all but extinct, and manufacturers had adopted PCI even for 486 computers. ISA continued to be used alongside PCI through 2000. Apple Computer adopted PCI for professional Power Macintosh computers (replacing NuBusNuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project, and eventually used by Apple Computer and NeXT Computer. It is no longer widely used. NuBus architecture NuBus was a considerable step for) in mid-1995, and the consumer PerformaThe Macintosh Performa series was Apple's consumer product line from 1992 until 1997, when the iMac's release ended this product line. The series was introduced in 1992 with the Performa 200, which was essentially a renamed Macintosh Classic II. Nearly ev product line (replacing LC PDSOther than " Party of Democratic Socialism", this also stands for "Processor Direct Slot". It was a solution (actually, a whole number of different solutions) introduced by Apple Computer, in several of their Macintosh models, to providing a limited measu) in mid-1996.

Later revisions of PCI added new features and performance improvements, including a 66MHz 3.3V standard and 133MHz PCI-X, and the adaption of PCI signalling to other form factors. With the introduction of the serial PCI-ePCI-Express (formerly known as 3GIO for 3rd Generation I/O is a new implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. It is being su standard in 2004, traditional PCI is likely to slowly die out.

2 Configuration

PCI devices are plug and play. The system firmware examines each device's PCI Configuration SpaceOne of the major improvements PCI had over other I/O architectures was its configuration mechanism. In addition to the normal memory-mapped and port spaces, it has configuration space . This is 256 bytes that is addressable by knowing the PCI bus, device and allocates resources. Each device can request up to six areas of memory space or I/O port space. They can also have an option ROM that can contain executable x86 or PA-RISC code, Open Firmware or an EFI driver.

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