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Cyrix 6x86 Microprocessor

Although Intel never produced chips termed 586s or 686s, the Cyrix 6x86 microprocessors were designed to compete with the Pentium 166 and the Advanced Micro Devices (AMD) K5 PR166, the so-called "Pentium killer". As with the AMD K5 and K6, Cyrix 6x86s received a P-rating that enabled the consumer to compare these clones to Intel Pentium performance, although internally, they are very different designs and not always compatible.

As the sixth x86-core chip generation fitted with 3 million transistors, Cyrix nicknamed the 6x86 the M1 (perhaps after the tank). The Cyrix 6x86 and 6x86L (low voltage) processors feature 16-kilobyte unified cache memories while the 6x86MX model has a 64-kilobyte cache. Utilizing doubling and tripling bus-to-core clock multipliers, Cyrix achieved higher performance with a smaller architecture. Featuring a 64-bit external data bus and a 32-bit internal address bus, bus speeds of 50 to 75 MHz were accelerated to 100 to 150 MHz clock speeds. By combining the best aspects of both reduced instruction set computing (RISC) specifications to reduce instruction cycle times and complex instruction set computing (CISC) specifications, the Cyrix 6x86 microprocessors excelled in performance through the superpipelined core.

Cyrix, a California Silicon Valley upstart, along with fellow clone masters Advanced Micro Devices, employed the reverse engineering concepts pioneered by the Japanese semiconductor industry to match and then leapfrog rival Intel's microprocessor innovations. Originally, Intel clones were built not on imitation, but rather on insecurity. IBM's huge financial risk with their barrier-breaking personal computers could not be allowed to depend solely on a fledgling Intel. Big Blue insisted that Intel license their patented designs to other worldwide manufacturers, so that the computer domineer would be guaranteed supply of the critical central processing units. Under a rather unique arrangement, Cyrix designed the chips and IBM manufactured them, with both marketing semiconductors carrying their own brand names.

Cyrix, with its partner IBM, continued the line with the 6x86L and 6x86MX processors with power ratings up to 233 MHz clock speeds, more refined fabrication techniques (from 0.65 down to 0.35 micron technology), and lower power dissipations. To avoid potential compatibility problems with older software, a hardware test without any modifications identifies a Cyrix 6x86 CPU as an unknown type of 486 chip, while the 6x86MX will be identified as a Pentium Pro model.

Contributing Authors

Omar Alvarado, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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