An enhanced PCI bus. PCI-X is backward-compatible with existing PCI cards. It improves upon the speed of PCI from 133 MBps to as much as 1 GBps. PCI-X was designed jointly by IBM, HP and Compaq to increase performance of high bandwidth devices, such as Gigabit Ethernet and Fibre Channel, and processors that are part of a cluster.
PCI-X (Peripheral Component Interconnect Extended) is a computer bus and expansion card standard designed to supersede PCI. It is essentially a faster version of PCI, running at twice the speed, and is otherwise similar in physical implementation and basic design. It has itself been replaced in modern designs by the similar-sounding PCI Express, which features a very different logical design.