PCI-X (Peripheral Component Interconnect Extended) is a computer bus technology (the "data pipes" between parts of a computer) that increases the speed that data can move within a computer from 66 MHz to 133 MHz. The technology was developed jointly by IBM, HP, and Compaq. PCI-X doubles the speed and amount of data exchanged between the computer processor and peripherals. With the current PCI design, one 64-bit bus runs at 66 MHz and additional buses move 32 bits at 66 MHz or 64 bits at 33 MHz. The maximum amount of data exchanged between the processor and peripherals using the current PCI design is 532 MB per second. With PCI-X, one 64-bit bus runs at 133 MHz with the rest running at 66 MHz, allowing for a data exchange of 1.06 GB per second. PCI-X is backwards-compatible, meaning that you can, for example, install a PCI-X card in a standard PCI slot but expect a decrease in speed to 33 MHz. You can also use both PCI and PCI-X cards on the same bus but the bus speed will run at the speed of the slowest card. PCI-X is more fault tolerant than PCI. For example, PCI-X is able to reinitialize a faulty card or take it offline before computer failure occurs.
IBM, HP, and Compaq designed PCI-X for servers to increase performance for high bandwidth devices such as Gigabit Ethernet cards, Fibre Channel, Ultra3 Small Computer System Interface, and processors that are interconnected as a cluster. Compaq, IBM, and HP submitted PCI-X to the PCI Special Interest Group (Special Interest Group of the Association for Computing Machinery) in 1998. PCI SIG approved PCI-X, and it is now an open standard that can be adapted and used by all computer developers. PCI SIG controls technical support, training and compliance testing for PCI-X. IBM, Intel, Microelectronics and Mylex plan to develop chipsets to support PCI-X. 3Com and Adaptec intend to develop PCI-X peripherals.
To accelerate PCI-X adoption by the industry, Compaq offers PCI-X development tools at their Web site.