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(Peripheral Component Interconnect eXtended) A 64-bit bus technology that is backward compatible with PCI and used in servers for high-speed networking and fast hard drives. PCI cards can be plugged into a PCI-X slot, and PCI-X cards can be plugged into a 32-bit PCI slot, even allowing part of the edge connector to hang over the slot, providing nothing on the motherboard is in its way.

Introduced in 1999 and developed by IBM, HP and Compaq, PCI-X offered more speed than PCI and steadily increased to more than 30 times that of the original PCI bus. The peak bandwidth of the PCI-X bus ranged from 133 to 4262 MBytes/sec. Although a greatly enhanced Version 2.0 was introduced in 2002, it was not widely used, and PCI-X in all its versions has been superseded by PCI Express (PCIe). For data rate comparisons of all PCI technologies, see PCI-SIG.

Some Name Confusion
PCI-X is also abbreviated PCX, which sounds like shorthand for "PCI Express." However, the official abbreviation of PCI Express is "PCIe." See PCI Express.

PCI-X Slots
PCI-X motherboards came with a mix of PCI and PCI-X buses. The long green slots are PCI-X, which accepted PCI-X and PCI cards. (Image courtesy of Giga-byte Technology Company Ltd., www.giga-byte.com)