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PCI Express Spec Updated

New areas include security and virtualization, according to the PCI Special Interest Group.
Designers think virtualization ultimately will be applied to all PC systems — even multitasking home computers. But its first target is server blades that are evolving towards stateless collections of compute boards in a single chassis linked on an Express mezzanine bus. The virtual I/O spec will allow those compute cards to share Express, Ethernet and storage I/O resources in and outside their chassis.

The spec is still in an early stage, with the 19-company working group about to put a requirements document out for review. A completed spec is not expected until late in 2006 or early in 2007. It will also require hardware changes for chip makers who want to support its features.

New form factors

While the security, virtualization and version 2.0 specs drive hardware changes for Express devices, three other efforts will bring existing Express connections to new applications.

One of the new applications is for a version of Express that runs over an external copper cable. The spec is seen as useful for any system that wants expanded I/O in a separate chassis. That includes some PC designs that might put a monitor, graphics and I/O in a desktop system and link to a desk-side system housing the CPU and hard disk. It could also be used by a server connecting to an optional I/O subsystem. Next-generation PCMCIA cards supporting Express slots may also want to use the cable to support links to other external devices.

The SIG has yet to define the type of cable it will employ and how long the cable will reach. Because the cable will support both today's 2.5 GHz and next year's 5 GHz Express versions, distance will in part depend on jitter and EMI issues still being characterized for the high-speed version.

"I think the cable will wind up being in single-digit meters, but as always someone could come along and build a repeater," said Pierce.

He emphasized that the cabled Express link is focused on use by OEMs connecting various subsystems. It is not seen as an end user interconnect that might compete with USB or 1394 interconnects.

Separately, the SIG is defining a wireless module for notebook computers. Designed to slide behind an LCD in a notebook computer's lid, the module takes up 2.5 times more area but only half the thickness of the mini-Express cards defined for use internally in PCs.

The module will house PHY and MAC silicon and be an attach point for multiple antennae for Wi-Fi and any other radios supported by the notebooks. The standard module is expected to ease problems notebook designers have had routing antennas from chips in a motherboard through a hinge and past the display with the interference from its video signals.

The wireless module standard is expected to be in a near-complete 0.9 version by this fall, paving the way for modules that could appear in 2006-class notebooks.

Finally, the SIG showed prototypes of Express Modules designed for rack-mounted servers. The modules are essentially card cages for either one or multiple half-sized Express adapter cards designed to be easily snapped into or out of server chassis without needing to access the internals of the server.

Marvell, Mellanox and QLogic showed prototype modules, respectively, for Ethernet, Infiniband and Fibre Channel adapters supporting four to eight Express channels.

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Brian T. Horowitz, Contributing Reporter
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Sara Peters, Editor-in-Chief, InformationWeek / Network Computing