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AMD & Cyrix Counter MMX

-- by David W. Methvin

Intel may be the driving force behind MMX, but competitors Advanced Micro Devices (AMD) and Cyrix aren't about to take a back seat. Both vendors will include Intel-compatible versions of MMX technology in their upcoming chips, and each plans to add features or capabilities that Intel lacks.

The two vendors will reportedly differentiate their offerings from Intel's by achieving Pentium Pro performance levels with their next-generation CPUs, while maintaining chip-socket compatibility with the Pentium. This approach is ideal for system makers because it doesn't require a motherboard change, but does offer a higher-performance option for buyers who want it. In addition, you may be able to update your current system from a low-end Intel Pentium to one of the new AMD or Cyrix chips without changing any other components.

AMD's new CPU, code-named AMD-K6, is scheduled to ship by this summer. As with Intel's Pentium Pro, the high chip speeds of the K6 require large and fast internal caches to keep things moving smoothly. The AMD-K6 includes a 32KB instruction cache and a 32KB write-back data cache. Its data cache is dual-ported so two loads or stores can occur in the same clock cycle. Seven parallel execution units (two load/store, two integer, floating-point, branch and MMX) can execute all or part of an instruction during a single clock cycle.

Cyrix's new CPU, code-named M2, is also targeted for release in the first half of this year. The M2 takes a slightly different approach to on-chip caching than the AMD-K6 or Pentium, using a single 64KB cache that holds both data and code. It incorporates additional specialized caches for branches, subroutine calls and address calculations. Like the AMD-K6, the Cyrix M2 allows two accesses to cache per clock cycle.

Risk Assessment

It's a bit too early to tell whether the AMD-K6 or Cyrix M2 chips will be a threat to the MMX-enabled Pentium or Pentium Pro. Neither vendor had more than spec sheets and slides to show at press time, and no PC makers have pledged to support the MMX alternatives. If AMD and Cyrix can deliver on their respective designs, the ability to upgrade existing Pentium systems to Pentium Pro performance levels with MMX technology could make these chips a great bargain-if you're willing to stray from "Intel Inside."

Copyright 1997 CMP Media Inc.

(From Windows Magazine, January 1997, page 232.)