Root complex
In a PCI Express system, a root complex device connects the processor and memory subsystem to the PCI Express switch fabric composed of one or more switch devices.
Similar to a host bridge in a PCI system, the root complex generates transaction requests on behalf of the processor, which is interconnected through a local bus. Root complex functionality may be implemented as a discrete device, or may be integrated with the processor. A root complex may contain more than one PCI Express port and multiple switch devices can be connected to ports on the root complex or cascaded.
