Peripheral Component Interconnect Express (PCIe, PCI-E)

Peripheral Component Interconnect Express (PCIe or PCI-E) is a serial expansion bus standard for connecting a computer to one or more peripheral devices.

PCIe provides lower latency and higher data transfer rates than parallel busses such as PCI and PCI-X. Every device that's connected to a motherboard with a PCIe link has its own dedicated point-to-point connection. This means that devices are not competing for bandwidth because they are not sharing the same bus.

Peripheral devices that use PCIe for data transfer include graphics adapter cards, network interface cards (NICs), storage accelerator devices and other high-performance peripherals.

With PCIe, data is transferred over two signal pairs: two wires for transmitting and two wires for receiving. Each set of signal pairs is called a "lane," and each lane is capable of sending and receiving eight-bit data packets simultaneously between two points.

Figure 1. PCI Express slots on a motherboard.

PCIe can scale from one to 32 separate lanes; it is usually deployed with 1, 4, 8, 12, 16 or 32 lanes. The lane count of a PCIe card is a determining factor in its performance and therefore in its price. For example, ann inexpensive PCIe device like a NICs might only use four lanes (PCIe x4). By comparison, a high-performance graphics adapter that uses 32 lanes (PCIe x32) for top-speed transmission would be more expensive.

PCIe bus slots are typically backward compatible with other PCIe bus slots, allowing PCIe links that use fewer lanes to use the same interface as PCIe links that use more lanes. For example, a PCIe x8 card could plug into a PCIe x16 slot. PCIe bus slots are not backwards compatible, however, with connection interfaces for older bus standards.

With PCIe, data center managers can take advantage of high-speed networking across server backplanes, and connect to Gigabit Ethernet, RAID and Infiniband networking technologies outside of the server rack. The PCIe bus also interconnects clustered computers that use HyperTransport.

For laptops and mobile devices, mini PCI-e cards can be used to connect wireless adaptors, solid state device storage and other performance boosters. External PCI Express (ePCIe) is used to connect the motherboard to an external PCIe interface. In most cases, designers use ePCIe when the computer requires an unusually high number of PCIe ports.

The PCI Special Interest Group defines, develops and maintains PCI Express standards.

Figure 2. The PCI Special Interest Group has a timeline for the development of PCI Express standards.
This was last updated in April 2015

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