PCI vs PCIe: Key Differences Explained

This article clarifies the distinctions between PCI (Peripheral Component Interconnect) and PCIe (PCI Express) bus interfaces, two fundamental technologies in computer architecture.

PCI Bus

PCI, short for Peripheral Component Interconnect, has been a mainstay in computer architecture for years.

The primary function of PCI is to provide a standardized interface for connecting various PC cards, such as video cards, sound cards, and network cards, directly to the motherboard. While these cards have seen significant advancements, the original PCI bus has remained relatively unchanged. PCI supports a bus width of 32 bits and can accommodate up to 5 devices simultaneously. PCI-X, a later iteration, extended the bus width to 64 bits.

However, the limitations of PCI led to the development of PCIe, designed to address its shortcomings.

PCIe Bus

PCIe, or Peripheral Component Interconnect Express, offers significant improvements over PCI.

This bus interface boasts higher bandwidth compared to PCI and enjoys broad operating system support. The PCIe architecture is designed to enhance overall computer speed and, in particular, delivers superior graphics performance. PCIe is fundamentally a serial connection, operating much like a network.

A PCIe system incorporates a switch that manages multiple point-to-point serial connections. In this architecture, each device has a dedicated connection, eliminating the bandwidth sharing inherent in traditional bus architectures. For instance, an x1 PCIe connection, utilizing a single “lane,” consists of 4 wires (2 for transmitting and 2 for receiving). This connection carries 1 bit per cycle.

Other PCIe configurations include x2, x4, x8, x12, x16, and x32, each offering progressively higher bandwidth. A x2 PCIe connection, for example, utilizes 8 wires and transmits 2 bits per cycle.

PCI vs PCIe: A Detailed Comparison

The following table outlines a detailed comparison between PCI and PCIe interfaces, focusing on aspects like speed, bus type, topology, and the number of devices supported.

For a deeper dive, also explore the advantages and disadvantages of PCI Bus and PCI Express.