"The switch has flipped. People just do not want to route 533-MHz PCI-X signals, and that's a sea change," said Chuck McManis, a technical director for storage system maker Network Appliance Inc. (Sunnyvale, Calif.).

"Basically, the speeds coming down the pike have necessitated going to serial interconnects," he said. "Interconnects like PCI-X and HyperTransport are suffering from the fact that they are getting harder to route the faster they go. We will do [serial] PCI Express using eight or 16 or however many lanes we need, though."

A senior computer interconnect engineer who asked not to be identified said he sees "a lack of activity in PCI-X at 266 MHz and above. It's difficult to handle jitter and skew at those speeds." By contrast, he said, "there's an enormous amount of effort going into PCI Express. Every major vendor is doing something with it."

"AMD came out with a system that could handle 266- and 533-MHz PCI-X last year, and that's about the only system I've seen doing 533 MHz," said Michael Krause, an interconnect specialist with Hewlett-Packard Co. Most of today's adapter cards will not need more than the 266-MHz data rates, Krause said.

Indeed, Al Yanes, president of the PCI Special Interest Group, said he does not see any activity in developing PCI-X beyond the current 533-MHz standard. The group is engaged in a lively debate, however, on whether the next-generation of PCI Express ought to go to 5 Gbits/second or 6.25 Gbits/s.