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The Cyrix 6x86MX® processor: Image courtesy of Cyrix Corporation

Along with AMD, Cyrix have fought a long and hard battle with Intel for a share of the lucrative "x86" processor market. From the days of the 386 and 486 clones (they really were clones of the Intel design) Cyrix have been lurking in the background of the CPU market. It was only with the release of the original 6x86+ chip in 1995 did Cyrix suddenly make a big splash into the CPU market.

A big splash though is never enough in this fast moving market and with the launch of the Intel Pentium MMX in 1997 Cyrix had to have a response. The 6x86MX was the chip to do just that and we have a look at what it has achieved and what it is still capable of as the now re-named Cyrix MII.

The Cyrix 6x86MX / MII

The 6x86MX was released shortly after the AMD K6 in the summer of 1997. It offered a similar performance advantage per clock speed over the Intel Pentium MMX as the original 6x86 did over the Pentium. This promised to be a very good little chip indeed. It built upon the strengths of the original 6x86 and tried to address some of its problems also.

The 6x86MX added MMX instructions to the existing core of the 6x86. Unlike AMD, Cyrix never had the right to call the processor "MMX" so instead had to make do with "MX" tagged onto the chip's name. Most people probably didn't notice the missing "M" from MMX, so this was no handicap for the chip. The 6x86MX is now called the Cyrix MII as a direct result of Cyrix terminating their foundry agreement with IBM who manufactured the processor and sold it too as the IBM 6x86MX. After National Semiconductor (Cyrix's new owners as of 1998) fabricated their own chips it was decided to re-name it the MII. This was in fact the original designation of the chip whilst it was in development but had the advantage of sounding like "Pentium II" and "K6-2" which were by then stealing all the limelight.

On the technical side the MII (as we shall now call it) boasted enhancements to its processor core over the original 6x86. Heat output was reduced allowing it to rise to clock speeds over 150 MHz and the chip utilised bus speeds of up to 83 MHz and later 100 MHz further boosting performance.

On the minus side though Cyrix still used the P Rating system of classifying processors even when AMD had moved away from it with the K6. Thus the MII never ran at the clock speeds it was designated to have with the PR166 running at 150 MHz and the PR333 only running at 250 MHz. That said the MII has P Ratings of PR 166, 200, 233, 266, 300 & 333.

To find out how sucessful this chip is, read on...


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© Copyright, Anthony Barrett 1999/2000.