Specifications for two new interconnection technologies were released yesterday by the PCI-SIG (peripheral component interconnect – special interest group) – PCI-X 2.0 for servers, and PCI Express for PCs.

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 completion of the testing process, the organization said. The Base specification and the Card specification for PCI Express were also released.

Product developers can begin designing products, such as interface cards and expansion slots that incorporate both technologies, PCI-SIG said. “The electrical portion needs to be tested for robustness”, but is otherwise complete, and there probably won't be significant changes from the release candidate to the final version, said Al Yanes, president of the PCI-SIG and a senior engineer for IBM's eServer Development Group.

Extra byte PCI Express is the next evolution of PCI technology, which allows internal components of a PC, such as the microprocessor, to communicate with devices – such as graphics cards – attached through expansion slots. 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 2.1GB per second. The other version, PCI-X 533, will allow transfer speeds of up to 533MHz, or data rates of up to 4.2Gbytes per second. Users of older PCI-X technology will be able to upgrade their 133MHz, 1.06GB per second, interconnect technology once product developers design add-in cards based on the specifications.

PCI Express will allow high-end graphics cards and other interconnects, such as USB 2.0 and Infiniband, to communicate with PCs at 2.5Gbps (bits per second) per lane per direction. Developers can build products using PCI Express with up to 32 lanes, providing additional bandwidth as required for their applications or products.

Slotting in 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. A PCI-to-PCI Express bridge, which would allow the Express cards to work in older slots, is in development by the Arapahoe Work Group.

PCI Express is designed to be scalable, and is a serial I/O (input/output) technology. Serial I/O technology has been used in other industry standards, such as Infiniband and Fibre Channel, and it allows for data to be exchanged more reliably over longer distances.