Exponential's Bid to Beat the Pack

Exponential Technology, a start-up company based in Silicon Valley, stands a good chance of breaking the 300-MHz barrier before the big names in the PowerPC alliance. Exponential is pinning its hopes on bipolar transistors, which can switch states much faster than conventional CMOS transistors; faster switching means higher clock speeds. Exponential's PowerPC 604-compatible chip (blessed with licenses from IBM and Motorola) uses bipolar transistors for almost all the logic, or about 40 percent of the chip's circuitry. The remaining 60 percent of the transistors are CMOS, mostly in the SRAM caches.

This radical new processor is on schedule to ship in the first half of 1997, the compa ny says. Exponential estimates peg initial clock speeds at 300 to 400 MHz, with 500 MHz a possibility by the end of next year (see "Watch Out: 500-MHz PowerPCs Planned for 1997," May BYTE, page 40).

Even more intriguing is a little-known U.S. patent Exponential won last January. Exponential won't talk about the patent, but it covers a technique for sharing a CPU's registers between two different instruction sets. This seems to indicate that Exponential is working on some kind of emulation technology. Could this be the spiritual descendant of IBM's PowerPC 615, which was supposed to run x86 software at native speeds? Sources say the 615 project is dead, but maybe Exponential is taking a different approach.

Another possibility is that Exponential is trying to integrate hardware support for 680x0 emulation in a PowerPC chip. Presumably the goal would be to run older Macintosh programs much faster than the software-based 680x0 emulator that Apple built into the Mac OS. ( Apple is a major investor in Exponential.) This theory seems less likely because the most important Mac software has already been ported to the PowerPC, and a bipolar CPU that runs at 300 to 500 MHz wouldn't need hardware assistance to emulate 680x0 software faster than a 68040 could run it natively.

For an in-depth report on how Exponential plans to achieve this speed breakthrough, see our exclusive coverage next month. [NOTE: This special feature article ("PowerPC Speed Demon") is available on our website at http://www.byte.com/art/9612/sec10/art1.htm .]