PCIe, or Peripheral Component Interconnect Express, is a high-speed serial computer expansion bus standard. It was designed to replace older standards like PCI, PCI-X, and AGP. PCIe provides a direct connection between the CPU and various expansion cards through dedicated lanes on the motherboard.
PCIe architecture is based on lanes, which are point-to-point serial connections. Each lane contains two pairs of wires: one pair for transmitting data and another for receiving data. This allows full-duplex communication. Multiple lanes can be combined to create wider connections, such as x1, x4, x8, or x16 configurations, with each additional lane doubling the available bandwidth.
The PCIe protocol uses a layered architecture similar to network protocols. At the top is the Application Layer where software and drivers operate. The Transaction Layer handles packet formation and addressing. The Data Link Layer manages error detection and correction. The Physical Layer controls lane management and flow control. Finally, the Electrical Layer handles the actual signal transmission over the physical wires.
PCIe has evolved through multiple generations, with each new generation doubling the data transfer rate. PCIe 1.0 started at 2.5 gigatransfers per second, providing 4 gigabytes per second for a 16-lane connection. The latest PCIe 5.0 reaches 32 gigatransfers per second, delivering up to 64 gigabytes per second of bandwidth for x16 slots. This exponential increase in bandwidth supports increasingly demanding applications.