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Definition: PCI

(1) (Payment Card Industry) See PCI DSS.

(2) (Peripheral Component Interconnect) A hardware interface for connecting peripheral devices to a computer. Introduced in 1993 and designed by Intel, Compaq and Digital Equipment, PCI superseded the ISA interface. PCI was widely used before it was superseded by PCI Express a decade later.

When first deployed, personal computers had several PCI slots; however, as time passed more computers used control circuits built into the motherboard chipsets, and the need for multiple slots diminished. Motherboards would later have only one PCI slot and an AGP slot for graphics. Eventually, PCI Express (PCIe) became the primary hardware interface for personal computers. See PCI Express and ISA.

PCI Made Life a Lot Easier
PCI eliminated conflicts that plagued the earlier ISA bus, which required an interrupt request (IRQ) number to be assigned to each ISA card. In contrast, the PCI bus architecture shares IRQs. Motherboards with both ISA and PCI were made for several years, and if there was only one IRQ left after the rest were assigned to ISA cards, all PCI devices could share it.

PCI Slots
PCI supports bus mastering, 32 and 64-bit data paths and runs at 33 or 66 MHz. The slot quantity is based on 10 electrical loads that deal with inductance and capacitance. The PCI chipset uses 3, motherboard controllers use 1, and plug-in cards use 1.5. For more slots, two PCI buses can be bridged. To compare data rates, see PCI-SIG. See bus mastering, PCI-X, Concurrent PCI, CompactPCI, PXI, PC data buses, PICMG and Sebring ring.

PCI Slots Are Not PCI Express (PCIe)
PCI sockets are not the same as PCIe. In addition, PCIe slots come in different sizes.

How PCI Is Connected
This illustration shows how the CPU, memory and peripherals are interconnected in a PC. Today's motherboards may not have any PCI slots. See PCI Express.