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PCI Express accelerates to 5Gbps

Posted: 01 Feb 2005 ?? ?Print Version ?Bookmark and Share

Keywords:pci special interest group? pci express?

The PCI Special Interest Group has voted to make 5Gbps the data rate for next-generation PCI Express, adding another multigigabit physical layer serial interconnect to a growing crowd.

Express is taking off rapidly in the PC, where it was initially aimed, but faces stiff competition among other link technologies in communications and storage networking gear.

The so-called Gen2 spec is scheduled to be finished by the end of 2005, and will hit the market in products by 2007. The group also investigated 5-, 6- and 6.25Gbps as possible next-generation speeds.

The 6.25Gbps speed aligns with next-generation Ethernet interconnects now coming on line from several vendors. It was also said to be favored by graphics companies hungry for maximum bandwidth. The 6Gbps rate was also favored by backers of Serial Attached SCSI (SAS), who selected that speed for their road map.

The electrical working group of the PCI SIG recommended 5Gbps for the next-generation data rate and a majority of the SIG's board voted for that rate, although the vote was not unanimous.

"There was a strong consensus from the board that this was the way to go," said Tony Pierce, chairman of the PCI SIG. Pierce characterized the months-long debate over the data rate as more of an in-depth analysis of complex risk factors.

"There are so many parameters to check when signaling rates get to this speed and that just takes time," Pierce said.

Pierce downplayed the notion that a decision in favor of 6.25Gbps would have created greater industry momentum by aligning computer and communications physical layers.

"Everybody wants a universal PHY, but that's impossible to spec," he said. PCI Express "does a lot of different things at the PHY layer. Other PHYs don't have power management or error checking at the link itself like we do."

The Gen2 version of Express is also expected to add a feature that lets systems automatically scale back from 5Gbps to the current 2.5Gbps data rate based on operating characteristics. Servers might scale back if thermals exceed certain thresholds while notebooks might slow down if they are running from battery power, Pierce suggested.

The anticipated move to 10Gbps Ethernet, Fibre Channel and 6Gbps SAS are driving the need for a faster version of Express, along with ever growing needs of digital media and graphics.

- Rick Merritt

EE Times

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