The PCI-X bus, PCI Extended, meets the increasing requirements of modern server technology. It was developed by Compaq, Hewlett Packard and IBM and is specified for a clock rate of 133 MHz. Inconjunction with the 64-bit bus, the original version of PCI-X achieves a data transfer rate of 1.1 GB/s.
PCI-X 2.0 achieves double the data transfer rate of 2.13 GB/s with the same bus width using DDR technology, Double Date Rate (DDR). With PCI-X 533 and PCI-X 1066, the PCI standard has two versions with data transfer rates of 4.2 GB/s and 8.5 GB/s respectively. In these versions, the clock frequency of 133 MHz is quadrupled. PCI-Express offers even higher transfer rates of 10 GB/s at a clock frequency of 1.25 GHz.
The PCI bus and PCI-X are compatible with each other. Since only one device can be operated at clock frequencies above 100 MHz, some motherboards are equipped with several PCI-X buses. PCI-X is also incompatible with PCI Express.