Cyrix 6x86 MX

by Anand Lal Shimpi on April 8, 1997 4:01 PM EST
When Intel announced that they were working on a successor to the Pentium with 57 new MMX instructions, AMD and Cyrix went head to head trying to develop the best Socket-7 processor on the market that could compete with Intel's flashy new chip. On April 2nd, AMD seemed to have won the race with the introduction of the K6, however about a month later, completely out of the blue, Cyrix released their 6th generation processor with MMX capabilities, code-named the M2 and eventually called the Cyrix 6x86MX.

In spite of the horrible name (6x86MX?!?!?! At least call it a 7x86 or something, but not 6x86MX) the 6x86MX is an excellent performing chip, it provides performance, for the most part, on par with the K6 and Pentium II under Windows 95. Unfortunately, like its predecessor, the 6x86MX has a VERY poor FPU, and therefore cannot compare with the Pentium MMX, K6, or Pentium II. But what gives the 6x86MX such awesome performance under Business applications? Lets find out...

  • 64KB of unified L1 Cache

  • Excellent Business Application performance

  • The BEST price to performance ratio when compared to all other 5th/6th generation processors

  • Many other features present in other more expensive 6th generation processors (i.e. AMD K6 or Intel Pentium II)

First Generation Cyrix 6x86MX Series Microprocessor
Chip Name P-Rating Clock Speed Bus Speed x Multiplier
Cyrix 6x86MX-PR2/166+ PR2/166 133MHz 66 MHz x 2.0
Cyrix 6x86MX-PR2/166+ PR2/166 150MHz 60 MHz x 2.5
Cyrix 6x86MX-PR2/200+ PR2/200 150MHz 75 MHz x 2.0
Cyrix 6x86MX-PR2/200+ PR2/200 166MHz 66 MHz x 2.5
Cyrix 6x86MX-PR2/200+ PR2/200 166MHz 83 MHz x 2.0
Cyrix 6x86MX-PR2/233+ PR2/233 188MHz 75 MHz x 2.5
Cyrix 6x86MX-PR2/233+ PR2/233 200MHz 66 MHz x 3.0

The first generation of the 6x86MX is quite unique when compared to the AMD K6 and Intel Pentium MMX/II. First of all, due to stability problems, Cyrix raised the voltage requirements of their entire 6x86MX line from 2.8v (like the Pentium MMX) to 2.9v (like the K6/166 and 200), although this may pose a problem to some people with motherboards that only have a 2.8v setting I can say from personal experience (with the MTech Mustang R534F which doesn't have a 2.9v setting) that the 6x86MX works extremely well at 2.8v although I cannot guarantee the utmost reliability at that setting. Cyrix once again has embraced the 75MHz bus speed, however this time around they didn't make it a requirement for their processors. Unlike the 6x86, the 6x86MX enables the user to use the 2.5x, 3.0x, and 3.5x clock multiplier settings in addition to the standard 2.0x. Therefore allowing the 6x86MX-PR2/166 which is designed to run at 133MHz (66 x 2.) to be run at 150MHz (60 x 2.5) or even 75 x 2.0 since you will be achieving the same clock speed while receiving performance equal to a 6x86MX-PR2/200+. The 6x86MX-PR2/200+ gives you even more "bang for your buck" since you can run it at a standard 66 x 2.5 (or even 75 x 2.0), or a stable yet unsupported 83 x 2.0!!! Finally, the 6x86MX-PR2/233+ can be run at 188MHz (75 x 2.5) or 200MHz (66 x 3.0), in either case the performance excellent with the 6x86MX...that is under business applications of course =)

Future Cyrix 6x86MX Series Microprocessors
Chip Name P-Rating Clock Speed Bus Speed x Multiplier Fab. Size
Cyrix 6x86MX-PR2/266+ PR2/266 225MHz 75 MHz x 3.0 ???
Cyrix 6x86MX-PR2/266+ PR2/266 233MHz 66 MHz x 3.5 ???
Cyrix 6x86MX-PR2/300+ PR2/300 263MHz 75 MHz x 3.5 ???
Cyrix 6x86MX-PR2/300+ PR2/300 266MHz 66 MHz x 4.0 ???

The future of the 6x86MX is quite hazy, since Cyrix merged with National Semiconductor they have announced that they will drop the high end line of processors and put more emphasis on low end processor solutions for the < $1000 PC. Regardless of what happens, at one point in time Cyrix had plans for the 6x86MX to make the move up to a PR2/300+ model and above you can see the possible clock speeds/PR2 ratings for any future 6x86MX CPUs.

If you like playing 3D games (*cough* Quake *cough*), or if you will use your system for heavy CAD or 3D rendering applications the Cyrix 6x86MX is definitely NOT for you. I only recommend using the 6x86MX for business applications or net surfing, if you expect to get high frame rates in Quake with the 6x86MX, think again! Even with a Monster 3D, the 6x86MX's performance is quite sad under Quake, so I wouldn't consider it much of a gaming CPU.

Windows 95 Performance of the Cyrix 6x86MX - Business Winstone 97

Chip Business Winstone 97
Cyrix 6x86MX-PR2/166+ (150/75) 54.0
Cyrix 6x86MX-PR2/200+ (166/66) 55.1
Cyrix 6x86MX-PR2/200+ (166/83) 56.3
Cyrix 6x86MX-PR2/233+ (188/75) Failed

Using the Shuttle HOT-569 as a test bed, we see that the Cyrix 6x86MX is a quite competitive processor, at 166MHz it provides business application performance on par with an AMD K6 running at 233MHz!!! As we have discovered with the 6x86, the 6x86MX achieves about a 2 - 3% increase in performance when using a motherboard/chipset that supports Linear Burst Mode SRAM transfers. In this case I used the MTech Mustang R534F using the SiS 5571 chipset, which supports Linear Burst Mode.

Windows 95 Performance of the Cyrix 6x86MX - Business Winstone 97
(Linear Burst Enabled)

Chip Business Winstone 97
Cyrix 6x86MX-PR2/166+ (150/75) 54.2
Cyrix 6x86MX-PR2/200+ (166/66) 56.3
Cyrix 6x86MX-PR2/200+ (166/83) Failed
Cyrix 6x86MX-PR2/233+ (188/75) Failed

Although we only notice a 0.2 Winstone points difference with the 6x86MX at 150MHz when using Linear Burst Mode, at 166MHz we get an increase of about 1.2 points, not bad for just capping one little jumper on the motherboard =) Using Mikael Johansson's latest beta of his superb 6x86 optimizer (which works perfectly with the 6x86MX) I re-ran the tests on the MTech board and came up with yet another increase in performance, take a look...

Windows 95 Performance of the Cyrix 6x86MX - Business Winstone 97
(Using 6x86OPT & Linear Burst)

Chip Business Winstone 97
Cyrix 6x86MX-PR2/166+ (150/75) 56.0
Cyrix 6x86MX-PR2/200+ (166/66) 57.6
Cyrix 6x86MX-PR2/200+ (166/83) Not Supported
Cyrix 6x86MX-PR2/233+ (188/75) Failed

Here the 6x86MX at 166MHz gets a business Winstone score higher than a K6/233 and very close to a Pentium II - 233!!! Kudos to Cyrix on a job well done, for the most part that is, take a look at the horrible High End Winstone scores below...

High End Windows 95 Performance of the Cyrix 6x86MX - High End Winstone 97

Chip High End Winstone 97
Cyrix 6x86MX-PR2/166+ (150/75) 22.7
Cyrix 6x86MX-PR2/200+ (166/66) 23.6
Cyrix 6x86MX-PR2/200+ (166/83) 24.3
Cyrix 6x86MX-PR2/233+ (188/75) Failed

Raw 6x86MX Performance - Wintune 97 Scores

Chip Millions of Instructions per Second (Integer) Millions of Floating Point Instructions per Second (FPU)
6x86MX (150/75) 292 65
6x86MX (166/66) 323 72

As you can tell by the Wintune 97 scores, FPU performance is the 6x86MX's major weakness, it is no where near the performance of the Pentium MMX's FPU not to mention the K6 and Pentium II, yet another reason not to consider the 6x86MX as a gaming processor.

Cyrix 6x86MX Gaming Performance - WinQuake Framerates

Resolution Cyrix 6x86MX-PR2/166 (150/75)
320 x 200 26.7 fps
512 x 384 14.7 fps
640 x 400 14.1 fps
640 x 480 12.4 fps
Resolution Cyrix 6x86MX-PR2/200 (166/66)
320 x 200 29.7 fps
512 x 384 15.4 fps
640 x 400 14.7 fps
640 x 480 12.9 fps

Ugh!!! That's all I need to say about the 6x86MX's Quake performance, this is NOT a processor for Quake fanatics, so if you are one scroll down and take a look at the Pentium MMX or Pentium II. Each processor has their own set of flaws, some are just more prominent than others, overall the 6x86MX is a very well designed chip worthy of your consideration.

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  • tipoo - Thursday, March 17, 2011 - link

    I just love these old articles
  • nhzero - Friday, October 23, 2015 - link

    I remember using this chip and playing Diablo. Those were the days!

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