PCI Express switch

A PCI Express switch routes transactions between PCI Express links in a hierarchy. In a conventional single-root arrangement, an upstream port connects toward the root complex and downstream ports connect toward endpoints or further switches. Software sees logical bridge relationships that describe this structure.^[ref]

For example, two devices can have separate downstream links while sharing one upstream link to the host. Their local links can operate independently, but simultaneous host-bound transfers compete for the upstream capacity. Adding ports does not manufacture unlimited host bandwidth. A PCI Express switch routes the interconnect's transactions; its role and addressing model differ from those of an Ethernet switch.