PCI-X PCI-X (Peripheral Component Interconnect Extended) is a new computer bus technology that increases the speed that data can move within a computer from 66 MHz to 133 MHz. 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
PCI-E
PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. It is being supported primarily by Intel, who started working on the standard as the Arapahoe project after pulling out of the InfiniBand system.