Introducing PCI Express

PCI Express, formerly codenamed 3GIO, is Intel's third-generation serial I/O bus architecture, which many hope will give data transport some extra oomph as the PCI bus runs out of steam.

It follows Intel's last bus technology, Next Generation I/O, now named InfiniBand.

When PCI Express is first implemented in workstations and notebooks in 2003, the bus will coexist with PCI and PCI-X slots. It connects to copper, fiber, and future media.

Dell is one systems vendor that plans to use PCI Express in servers and workstations. "We're bullish on PCI Express," says Jimmie Pike, director of architecture for Dell's Enterprise Systems Group.

PCI Express is not meant to replace InfiniBand as an interconnect for server clusters. PCI Express will instead be used to connect storage and network devices to a server. It replaces the current PC architecture in which the memory attaches to the North Bridge in the processor, which in turn connects via a proprietary interface such as the Intel Hub architecture to the PCI or PCI-X bus. In PCI Express, the memory still attaches to the processors' North Bridge, but that in turn connects to the 3GIO bus and eliminates proprietary components. Both the PCI-X and 3GIO buses attach from there to the fabric interconnect, whether it is InfiniBand, Ethernet, Universal Serial Bus or Texas Instruments' high-speed 1394b bus.

PCI Express uses pairs of differential low-voltage signals running at 2.5G bit/sec or an individual pin rate of 100M bit/sec. Manufacturers can add additional pairs to further push performance.

Dell's Pike says technologies like video-on-demand that require I/O greater than a gigabit per second will require PCI Express. These include 10 Gigabit Ethernet, which is already shipping. Compaq, Intel, Dell, Hewlett-Packard, IBM and Microsoft all support PCI Express.

PCI Express is now being reviewed by the members of the PCI-SIG for standardization.

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