PCI Express 3.0 is comming

Separately vendors now have a cabled version of PCI Express 1.1 up and running. PLX Technology showed cabled Express linking two separate chassis to expand the number of I/O cards that could be supported by one server. One Stop Systems (Escondido, Calif.) although not exhibiting at the conference is shipping a variety of designs using cabled Express.

In addition, the PCI SIG is developing a standard to support high-end graphics cards that dissipate as much as 300W, up from 150W today. A final spec could be ready by the end of the year.

The PCI SIG is also making progress on an effort to create a standard for I/O virtualization over Express. The ability to create separate software partitions on a system through virtualization has been one of the hot features that has emerged in mainstream computing with the rise of multicore processors.

The group finished in March a standard for an address table lookup feature that is the basis of the spec. A standard for implementing I/O virtualization in single CPU systems should be finished in the fall, and one for multiprocessing systems should be done before the end of the year.

Looking ahead, the PCI SIG is working on several fronts to define a version 3.0 for Express that could appear in products in late 2009. Engineers are still debating whether it will target 8 or 10 G transfers/second. The higher rate might break compatibility with the 1.1 version of Express, while the slower option might not be compelling enough to drive industry adoption.

Engineers are characterizing a number of parameters for how to implement the spec this year with the aim at settling on a set of those parameters sometime in 2008. Their overarching goal is to define a spec that can be cost effective for high volume manufacturing leveraging 65nm silicon.

"There's a lot of simulation work going on now," said Ramin Neshati, an Intel engineering manager who chairs a group overseeing serial technologies for the PCI SIG.

Another working group is exploring changes at the transaction layer for Express 3.0 to lower latency at least ten percent while raising actual delivered bandwidth. Due to encoding and protocol overhead, version 2.0 typically achieves only about 70 percent of its theoretical 5 Gbits/s throughput. Two other groups are considering changes for version 3.0. One is working on ways to reduce the data rates or link widths of Express devices while still handling useful work. Another is exploring ways to work with operating systems and device drivers to more effectively execute Express commands.

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