Cyrix 6x86MX

Cyrix’s response to Intel’s MMX technology was the 6x86MX, launched in mid-1997, shortly before the company was acquired by National Semiconductor. The company stuck with the Socket 7 format for its new chip, a decision which held down costs to system builders and ultimately consumers by extending the life of existing chipsets and motherboards.

The architecture of the new chip remains essentially the same as that of its predecessor, with the addition of MMX instructions, a few enhancements to the Floating Point Unit, a larger 64KB unified primary cache and an enhanced memory-management unit. Its dual-pipeline design is similar to the Pentium’s but simpler and more flexible than the latter’s RISC-based approach.

The 6x86MX was well-received in the marketplace, with a 6x86MX/PR233 (running at a clock speed of 187MHz) proving faster than both a 233MHz Pentium II and K6. The MX was also the first leading processor capable of running on a 75MHz external bus, which provides obvious bandwidth advantages and boosts overall performance. On the downside, and in common with previous Cyrix processors, the 6x86MX’s floating-point performance was significantly less good than that of its competitors, adversely affecting 3D graphics performance.

The Cyrix MII is an evolution of the 6x86MX, operating at higher frequencies. By the summer of 1998 0.25-micron MII-300 and MII-333 processors were being produced out of National Semiconductor’s new manufacturing facility; in Maine and the company claimed to have already seen shrinks of its 0.25-micron process to produce 0.22-micron geometries on its way to its stated goal of 0.18 micron the following year.

However by 1999, while AMD and Intel were leapfrogging one another in clock speeds, reaching 450 MHz and beyond, National Semiconductor were in financial trouble and Cyrix were lagging well behind their rivals, taking almost a year to push the MII from PR-300 to PR-333. It was no great suprise therefore when in August of that year, Cyrix finally bowed out of the PC desktop business, with National Semiconductor selling the rights to its x86 CPUs to Taiwan-based chipset manufacturer VIA Technologies.