Stands for "Peripheral Component Interconnect Extended." Once again, "Ex" is abbreviated with an "X" instead of an "E." Most desktop computers include one or more PCI slots for expanding the computer's I/O capabilities. Common PCI cards include network cards, sound cards, and video cards. In the early 1990s, when PCI was first introduced, the 66 MHz speed of PCI was more than sufficient for PCI cards available at the time. However, a decade later, expansion cards supported much faster data transfer rates and therefore became faster than the PCI bus would support. To prevent the interface from becoming a bottleneck, PCI-X was introduced.
The first version of PCI-X supported data transfer rates of 133 MHz, which is more than twice as fast as the original PCI standard. Then along came PCI-X 2.0, which can run at speeds of 266 or 533 MHz. These speeds are fast enough to support Gigabit Ethernet cards and video capture devices without slowing them down. PCI-X cards can only be installed in PCI-X slots, but the slots themselves are backwards compatible with PCI cards.