PCI Express root port

A PCI Express root port is a port in a root complex that starts a PCI Express link leading toward downstream devices or a switch. The PCI Express root port is represented as a logical bridge in the hierarchy. It is distinct from the PCI Express endpoint that provides a device function.^[ref]

For example, a storage PCI Express endpoint can attach directly to one PCI Express root port, while another root port connects to a switch serving several devices. Port services such as error reporting, hot plugging or power management concern that hierarchy and its links. Requiring a root-port service driver is therefore a different task from writing the device driver for the storage endpoint.