Introduction

PCIe (Peripheral Component Interconnect Express) is a bus standard that replaced PCI and PCI-X. PCI-SIG (PCI Special Interest Group) creates and maintains the PCIe specification.

PCIe is used in all computer applications including enterprise servers, consumer personal computers (PC), communication systems, and industrial applications. Unlike older PCI bus topology, which uses shared parallel bus architecture, PCIe is based on point-to-point topology, with separate serial links connecting every device to the root complex (host). Additionally, a PCIe link supports full-duplex communication between two endpoints. Data can flow upstream (UP) and downstream (DP) simultaneously. Each pair of these dedicated unidirectional serial point-topoint connections is called a lane. The PCIe standard is constantly under improvement,with PCIe 3.0 being the latest version of the standard.

Other important features of PCIe include power management, hot-swappable devices, and the ability to handle peer-to-peer data transfers (sending data between two end points without routing through the host). Additionally, PCIe simplifies board design by utilizing serial technology, which eliminates wire count of parallel bus architectures.

The PCIe link between two devices can consist of 1–32 lanes. The packet data is striped across lanes, and the lane count is automatically negotiated during device initialization.

The PCIe standard defines slots and connectors for multiple widths: X1, X4, X8, X16, X32. This allows PCIe to serve lower throughput, cost-sensitive applications as well as performance-critical applications.