What is PCI Express?

PCI-X or PCI Express Protocol

     PCI-SIG has released the protocol portion of the PCI-X (PCI-Extended) specification, as well as the "release candidate" for the electrical portion of the specification. The electrical portion is still being tested, and will be released upon the completion of the testing process in the coming weeks, the organization said. The Base specification and the Card specification for PCI Express were also released.
     Product developers can now begin designing products, such as interface cards and expansion slots that incorporate both technologies, PCI-SIG said.
     PCI Express is the next evolution of PCI technology, which allows internal components of a PC, such as the microprocessor, to communicate with devices attached through expansion slots, like graphics cards. PCI-X is a bus technology used within computers to allow chips to exchange data at faster speeds than PCI technology allows.
     Two versions of the PCI-X 2.0 technology will be released. PCI-X 266 can move data within a computer at speeds of up to 266MHz, allowing data rates of up to 2.1G bytes per second. The other version, PCI-X 533, will allow transfer speeds of up to 533MHz, or data rates of up to 4.2G bytes per second. Users of older PCI-X technology will be able to upgrade their 133MHz, 1.06G bytes per second, interconnect technology once product developers design add-in cards based on the specifications released to PCI-SIG members on the organization's Web site. (http://www.pcisig.com)
     PCI Express will allow high-end graphics cards and other interconnects such as USB (universal serial bus) 2.0 and Infiniband to communicate with PCs at 2.5Gbps per lane per direction.
     PCI-X is fully backwards-compatible with PCI, meaning that PCI-X cards can be plugged into PCI slots, and software written for PCI-X will work on PCI-equipped PCs. However, the PCI-X cards will exchange data at PCI speeds when plugged into PCI slots.
     PCI Express is software-compatible with PCI, but represents a new direction for the hardware side of the technology, and PCI Express cards will not work in PCI slots. It is designed to be scalable, and is a serial I/O (input/output) technology.

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