"Redwood is the best implementation of a high-speed physical-layer interface I have seen," said Peter Glaskowsky, editor of The Microprocessor Report. "I was amazed at how fast they have it running, and their skew recovery mechanism is very effective."

Redwood could be used in an array of designs and has a shot at replacing the implementation underpinnings of the follow-ons for today's SPI-4, PCI-X, RapidIO or HyperTransport links, Glaskowsky said. Early last month, Rambus (Los Altos, Calif.) said it had already licensed the technology to Sony and Toshiba for their so-called Cell processor being designed for the next-generation Playstation.

"That could be a bigger deal for Rambus than the RDRAM agreement with Intel, because Sony ultimately could use Cell across its entire product line. The Cell design win alone will convince people to look at the technology," Glaskowsky said.

Others remain skeptical.

Brian Holden, chairman of the HyperTransport consortium's technical working group and a principal engineer at PMC-Sierra Inc., said his group has not fully evaluated the technology yet.

Designers have started discussions on HyperTransport 2, a backward-compatible version of the parallel bus that would take it to data rates in the range of Redwood. But "it is often difficult to achieve backward compatibility against a full set of I/O specifications with a dramatically different I/O cell," Holden said.

"The trend in interfaces is to open, standard technologies," said Dan Bouvier, PowerPC architect at Motorola and one of the designers of the RapidIO interface.

Standards groups like RapidIO will not tie their specs to proprietary technologies like Redwood, Bouvier said, and for now Motorola sees no use for Redwood in PowerPCs. But he did say the development shows parallel buses will coexist with serial links for years because parallel interconnects offer advantages in latency, cost and die size. Indeed, Glaskowsky said, some new serial interconnects display inherent inefficiencies.

Redwood can be used on existing BGA and flip-chip packages and tolerates the impedance swings of 15 percent found on common four-layer pc boards.

Rambus will license Redwood as intellectual property in a manner similar to its existing memory and serdes technologies. The company will charge an upfront non-recurring engineering fee and a per-unit royalty fee that will vary based on the complexity and volume-sales expectations of chips using the technology.