Exponential drives PowerPC up and over 500MHz

The Macintosh has again eclipsed the PC in raw horsepower: start-up chip maker Exponential Technology has developed the X704 processor, which boasts a blazing core speed of 533MHz.

The Macintosh has again eclipsed the PC in raw horsepower: start-up chip maker Exponential Technology has developed the X704 processor, with a blazing core speed of 533MHz. Expected to ship in the second quarter of 1997, the CPU will also be available in 466MHz and 500MHz versions. And although Intel has said the Pentium class will graduate to clock speeds of 200MHz and above sometime in 1997, no specific time frame for delivery has been announced.

Industry analysts and vendors acknowledge Exponential's innovation - it puts some new twists on traditional CPU design - but many are uncertain about whether the new chip can give the PowerPC platform a needed leg up on the competition.

The X704 uses BiCMOS technology, which combines bipolar CPU design - a speed-enabling holdover from the world of powerful mainframes - with the CMOS technology common in today's processors, but it uses a greater number of bipolar cells than other BiCMOS implementations. In short, bipolar logic is much faster than CMOS.

However, the experts say that Exponential still needs to prove itself on several counts. As Eric Lewis, a researcher with International Data Corporation, puts it, "You don't just take a 500MHz chip and plunk it down into a box. Heat, bus speed, cache - all these things have to be tuned."

Exponential says it carefully considered exactly these issues to provide a thoroughbred processor. Rick Bergman, vice president of marketing, points to its simple yet effective solution for dissipating the heat generated by the increased power consumption of bipolar logic: use existing fans, but add ducts to channel the airflow directly over the heat sink. And he claims that the CPU's dual-caching system will enable the X704 to run at 500MHz in spite of current limitations in bus speeds (typically 50MHz in today's Macs).

Many vendors of high-speed processors turn to caching systems to improve application performance in light of bus bottlenecks, but the X704, which will plug into existing machines via a special daughtercard, will include a 2Kb Level 1 data cache, a 2Kb Level 1 instruction cache, and a 32Kb Level 2 cache - all on the CPU itself. Most CPUs contain only Level 1 cache, with Level 2 cache residing on the board. Essentially, Exponential's scheme adds a third level of cache, since on-board Level 2 cache will still be available.

Of course, while additional cache can improve the performance of nearly any application, it's no substitute for greater bus speed. According to Motorola, we'll begin to see 75MHz buses during the life cycle of its next-generation PowerPC CPU, the G3 series, due out in midyear.

As to whether Exponential will be able to provide an attractive price/ performance ratio, Bergman maintains that the cost for all this innovation will be relatively low, particularly given its target market of high-end graphics users. When sold in volume, the chip/ card combination will be US$1000, a premium that CPU makers will pass along to users, though consumer pricing has yet to be determined. Exponential believes high-end graphics users will be happy to pay for the performance jump. Market researcher Nathan Brookwood of Dataquest agrees: "A little improvement in productivity is worth a lot of money to designers or to their employers." Currently, a 200MHz PowerPC 604e processor sells for about $570. And although production problems have stemmed the flow of higher-speed 604s, Bergman is confident that by the end of the second quarter this year Exponential will be able to produce the X704 in volume.

Clone vendors including Power Computing and Umax, as well as Apple Computer, endorse the Exponential effort.

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