PCI bus picks up speed

With faster RISC and Pentium Pro processors on the horizon, many chip set and system vendors are developing a more robust version of the PCI bus architecture that will double the I/O throughput for high-end systems to 267Mbit/s.

According to sources at companies planning to build products around the faster designs, chip sets enabling a 64-bit version of the PCI bus architecture will appear in Pentium Pro, PowerPC, MIPS, and Cyrix 6x86 and 7x86 systems.

Those systems and related peripherals are slated to appear at next quarter's Comdex. System vendors that are expected to at least demonstrate the technology at the November show in Las Vegas include IBM, Digital Equipment and Apple, sources say.

Even Intelis expected to support 64-bit PCI by the time Comdex rolls around.

Although Intel has consistently said the market doesn't need 64-bit PCI yet -- and has been positioning its Accelerated Graphics Port (AGP) architecture as an alternative to faster PCI buses -- some sources are indicating that the company will tacitly support the faster design, because it will improve throughput for systems using its top-of-the-line Pentium Pro processors.

"Right now PCI is not the bottleneck, but when faster processors come out, it will be," one manufacturer says.

Digital already offers a 64-bit PCI chip set for its Alpha RISC processor line, which runs as fast as 400 MHz. Pentium Pro and PowerPC chips approaching those speeds are expected to ship in early 1997. Some of the chip set vendors supporting 64-bit PCI include IBM, Motorola, VLSI Technology and two Taiwanese companies: United Microelectronics and Winbond Electronics, sources say.

A number of graphics companies, including S3 and 3Dlabs, are already developing products to take advantage of the forthcoming PCI architecture.

The move to 64-bit PCI will cap a long technical and political struggle over the future of the industry-standard I/O bus. Intel, the original developer of the PCI standard, developed the AGP interface to give itself a short-term advantage over RISC-based systems in low-cost graphics performance.

Technical issues have also delayed faster PCI designs, because 64-bit versions of the bus require more pin-outs at a higher cost and backward compatibility is hard to achieve, some developers say.

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