What Is PCI? Peripheral Component Interconnect

PCI Bus Connects Peripherals to the Motherboard

PCI is an abbreviation for Peripheral Component Interconnect, which is a term used to describe a common connection interface for attaching computer peripherals to a PC's motherboard, or main circuit board. It is also called a PCI bus. A bus is a term for a path between the components of a computer.

Most often, a PCI slot was used to connect sound and network cards. PCI at one time was used to connect video cards, but graphics demand from gaming made it inadequate for that use. PCI was popular from 1995-2005 but was generally replaced by other technology such as USB or PCI Express. Desktop computers after that era may have PCI slots on the motherboard in order to be backward compatible. But the devices that used to be attached as PCI expansion cards are now integrated onto motherboards or attached by other connectors such as PCI Express (PCIe).

  • Also Known As: Peripheral Component Interconnect, PCI Bus, Conventional PCI
  • Not to Be Confused With: PCI compliance, which stands for payment card industry compliance, and PCI DSS which stands for payment card industry data security standard.

PCI Connects Peripherals to the Motherboard

A PCI bus lets you change different peripherals that are attached to the computer system. It allowed using different sound cards and hard drives. Usually, there were three or four PCI slots on the motherboard. You could simply unplug the component you want to swap and plug in the new one in the PCI slot on the motherboard. Or, if you have an open slot, you can add another peripheral. Computers may have more than one type of bus handling different types traffic. The PCI bus came in both 32-bit and 64-bit versions. PCI runs at 33 MHz or 66 MHz.

PCI Cards

PCI cards exist in several shapes and sizes called form factors. Full-size PCI cards are 312 millimeters long. Short cards range from 119 to 167 millimeters to fit into smaller slots. There are further variations such as compact PCI, Mini PCI, Low-Profile PCI, etc. PCI cards use 47 pins to connect. It supports devices that use 5 volts or 3.3 volts. 

Peripheral Component Interconnect History

The original bus that allowed expansion cards was the ISA bus invented in 1982 for the original IBM PC and was in use for decades. Intel developed the PCI bus in the early 1990s. It provided direct access to system memory for connected devices via a bridge connecting to the frontside bus and eventually to the CPU.

PCI became popular when Windows 95 introduced its Plug and Play (PnP) feature in 1995. Intel had incorporated the PnP standard into PCI, which gave it the advantage over ISA. PCI didn't require jumpers or dip switches as ISA did.

PCI Express (Peripheral Component Interconnect Express) or PCIe improved on PCI and has a higher maximum system bus throughput, lower I/O pin count and is smaller physically. It was developed by Intel and the Arapaho Work Group (AWG). It became the primary motherboard-level interconnect for PCs by 2012 and replaced AGP as the default interface for graphics cards for new systems.