PCI Express Moves Closer to Your PC

Tuesday, PCI-SIG (Peripheral Component Interconnect-Special Interest Group) released pecifications for two new interconnect technologies--PCI-X 2.0 for servers, and PCI Express for PCs--the group announced.

PCI-SIG has released the protocol portion of the PCI-X (PCI-Extended) specification and 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, the organization said. The organization also released the Base specification and the Card specification for PCI Express.

Product developers can now begin designing products, such as interface cards and expansion slots that incorporate both technologies, the PCI-SIG announcement said. "The electrical portion needs to be tested for robustness," but otherwise it is complete, and there probably won't be significant changes from the release candidate to the final version, according to Al Yanes, president of PCI-SIG and a senior engineer for IBM's EServer Development Group. Developers will spend more time on the protocol portion, which is why PCI-SIG released it as soon as it was completed, Yanes says.

Expanding Your Options

PCI Express is the next stage of PCI technology, which allows internal components of a PC (such as the microprocessor) to communicate with devices like graphics cards that are 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 266 MHz, allowing data rates of up to 2.1GB per second. The other version, PCI-X 533, will allow transfer speeds of up to 533 MHz or data rates of up to 4.2 GBps. Users of older PCI-X technology will be able to upgrade their 133-MHz, 1.06-GBps interconnect technology once product developers design add-in cards based on the specifications released to PCI-SIG members on the organization's Web site.

PCI Express will allow high-end graphics cards and other interconnects such as USB 2.0 and Infiniband to communicate with PCs at 2.5 gbps 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.

Working Together

PCI-X is fully backward-compatible with PCI, so PCI-X cards can be plugged into PCI slots, and software written for PCI-X will work on PCI-equipped PCs. However, PCI-X cards will exchange data at PCI speeds when plugged into PCI slots.

PCI Express is software-compatible with PCI, but it 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, Yanes says. Because PCI-SIG does not own that development process, Yanes is unable to comment on a time frame for the bridge's release.

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