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Cyrix 6x86 (M1)

Introduction date
Introduction speed
Maximum speed
Transistor count
Manufacturing process

: Cyrix
: IBM, SGS-Thomson, NS
: Februari 1996
: PR120+ (100Mhz)
: PR200+ (150Mhz)
: 16 Kb Level 1
: 3.3 million
: 0.65 & 0.35 micron

After the 80486, Intel introduced the Pentium as their next generation CPU. Other manufacturers were also designing their Pentium equivalent, AMD was designing the K5 and Cyrix had their 6x86. The design of the CPU was very advanced at its time, while it had a 5th generation design some 6th generation technologies were implemented. These enhancements made the 6x86 (codename M1) a powerful CPU, integer performance of the 6x86 was much better than the Pentium on a clock for clock basis. So much that Cyrix decided to use a performance rating, the CPU ran at lower clock speeds but performed like a Pentium at higher clock speed.

Cyrix had designed a great CPU but could not manufacture it themselves. Cyrix was a so called fables company and had to rely on third parties to manufacture its designs. Cyrix closed a deal with IBM and SGS-Thompson (ST) to manufactured the 6x86. Part of that deal was that IBM and ST could sell the 6x86 under their own name for a modest royalty fee. Unfortunately the 6x86 was not manufactured with the most modern production facilities. It was manufactured at 0.65 microns while Intel used 0.50 micron technology with the Pentium. This lead to a much heard complaint about Cyrix CPU's, they ran very hot. Later when the production was switched to 0.35 micron lower voltages could be used. 6x86's produced with that technology were named 6x86L where the L stands for low voltage.

The performance of the 6x86 was very good compared to a Pentium. This was, by the way, only true for the integer performance. The floating point performance was far behind that of a Pentium, which is strange because Cyrix designed the fastest math coprocessors for the 286 and 386. While designing the 6x86 the decision was made to use more transistors for the Integer unit of the CPU, the FPU had to do with less transistors which made it less powerful. Floating point calculations are hardly used in everyday use, so the less powerful FPU was no problem. Only hardcore gamers and CAD/CAM users made intensive use of that part of the CPU.

Speeds were gradually increased and the last version, the PR200+ (150MHz), was the fastest CPU around when it came out. It used a bus speed of 75MHz which was unheard of, all other CPU's used 60 or 66MHz. Problem with that bus speed was to find a board that would run stable enough, but a good board teamed up with the 6x86 PR200+ was an unbeatable combination.

The 6x86 was typically packed in a PGA and needed a heatsink and fan to operate. It was pin compatible with the Pentium and will fit in standard Socket5 and 7 motherboards. Although the design of the CPU was very good, it had some compatibility problems. This was not because of Cyrix but because programmers wrote software for Intel CPU's, and Intel used some extra instructions. This made it look like Cyrix CPU's were not 100% x86 compatible, but the real story was that the software was not 100% x86 compatible!

Available models :

6x86 PR90 (80MHz), 2 x 40MHz
6x86 PR120 (100 MHz), 2 x 50MHz
6x86 PR133 (110 MHz), 2 x 55MHz
6x86 PR150 (120 MHz), 2 x 60MHz
6x86 PR166 (133 MHz), 2 x 66MHz
6x86 PR200 (150 MHz), 2 x 75MHz

All Cyrix 6x86 pictures

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