PCIeSwitches

PCIe switches are devices that expand PCI Express connectivity by interposing a switch between a single PCIe root complex and multiple endpoints or other switches. A PCIe switch provides one upstream port and multiple downstream ports, effectively creating a PCIe fabric that can fan-out a root port to several devices. The switch routes PCIe transaction layer packets to the correct downstream port using an internal routing table and address map, and it handles functions such as enumeration, power management, and quality of service as supported by the device.

In operation, the upstream link negotiates speed and lane width with the root complex, while each downstream link negotiates separately with its attached device or another switch. PCIe switches may be standalone devices or embedded into system-on-chip designs or motherboard implementations. They support varying numbers of downstream ports and can be chained to form larger fabrics. Features in higher-end models may include advanced routing options, error containment, hot-plug support, and, in some cases, access control services to prevent misrouted transactions.

Common use cases include expanding the number of PCIe endpoints in servers, workstations, storage controllers, and networking devices; connecting PCIe NVMe drives, accelerators, or GPUs to a single root complex; and building modular systems with removable components. PCIe switches conform to the PCI Express specification and are designed to preserve PCIe transaction semantics across the fabric. Evaluation criteria typically include port count, lane width and generation support, latency, and power consumption.