A computer system is described having a plurality of processing nodes interconnected by a first point-to-point architecture, and a system memory including a plurality of portions each of which is associated with one of the processing nodes. Each processing node includes a processor, and a memory controller for controlling access to the associated portion of the system memory, and may contain a host bridge for facilitating communication with a plurality of I/O devices. The first point-to-point architecture is operable to facilitate first transactions between the processors and the system memory. The computer system further includes at least one I/O controller and a second point-to-point architecture independent of the first point-to-point architecture and interconnecting the I/O controller and the host bridges. The at least one I/O controller is operable to facilitate second transactions between the I/O devices and the system memory via the second point-to-point architecture.