Cyrix M-II 300

by Anand Lal Shimpi on May 26, 1998 3:08 PM EST
Intel and AMD are battling for the most cost effective processor solution for the home user.  Both are claiming outstanding gaming performance, excellent business application speed, and both are arguing over who is faster.  Observing from a distance is none other than the popular low-cost processor manufacturer, Cyrix.  After the initial fame the successful 6x86 processor brought Cyrix, the fab-less manufacturer decided it was time for a more powerful successor.   While everyone expected the successor to the 6x86 to be a much more powerful processor geared towards the high end market while making sure that gamers weren't left out, no one was truly surprised when the long awaited successor turned out to be nothing more than a higher clock speed processor with more L1 cache and MMX instructions.  So went the introduction of the 6x86MX... Cyrix M-II 300 Review
Much more of a disappointment than its predecessor, the 6x86MX demanded that the market be given an alternative solution to cover up its shortcomings.  Unfortunately for Cyrix, that alternative came from AMD with the K6.  Simply hating being the last to jump on any bandwagon, Cyrix decided to push the limits of their current microprocessor architecture once again.  Exactly one day before Intel announced the release of their first processors with support for the 100MHz Front Side Bus, Cyrix made a press release about their next generation 6x86MX CPU, the M-II, with support for the 100MHz FSB.  A trick like this has been known to be in Cyrix's mystery bag, tracing back to the days of the original 6x86 when Cyrix pushed the FSB limits past the officially supported 66MHz clock to 75MHz with their PR-200+.

The press release Cyrix made about their new M-II processors was a bit disappointing to most Cyrix advocates that expected a revamped Floating Point Unit and higher clock speeds from the next generation 6x86MX.  The M-II became known as nothing more than a faster 6x86MX with a new name that surprisingly enough resembled the P2 in the simplicity of its nomenclature. 

The M-II, like the original 6x86 and 6x86MX isn't identified by its clock speed, rather by its performance rating number.  For example, the M-II 300 doesn't actually run at 300MHz rather provides business application performance generally greater than or equal to a 300MHz 6th generation processor such as the Pentium II or the K6-2.  In actuality the M-II 300 operates at a 233MHz clock frequency however it can be run at anywhere from 200MHz (100 x 2.0) to 233MHz (66 x 3.5) including 208MHz (83 x 2.5) and 225MHz (75 x 3.0) making the M-II a processor whose versatility is encouraged to be taken advantage of by the manufacturer themselves.   Officially the M-II 300 only supports operation at 233/66 however the above settings will work perfectly fine with the processor as long as the other components in your system have no problem with the increased FSB frequency.

Set apart by its unified 4-way set associative 64KB L1 cache (generally the L1 cache is split equally into two parts, data and instruction set cache) the M-II uses the same exact core found in the 6x86MX processor, meaning you get the same processor with a new name and a higher clock speed.   The operating voltage of the M-II, like previously 6x86MX processors and the AMD K6 166/200, is 2.9v which makes the M-II an option for a great number of users with motherboards a year old.  If your motherboard doesn't support the 2.9v core voltage then you may be out of luck, while the processor can work at 2.8v and 3.0/3.1v doing so isn't encouraged by the manufacturer.  The 2.8v setting will only work if you have a very well designed motherboard (from an engineering perspective), if the 2.8v setting on your board fluctuates beyond a reasonable range then you will probably experience quite a bit of instability.  The same goes for the 3.0/3.1v settings, so your best bet for the M-II would be to get it with a board that officially supports it.

The chip itself bears the new M-II logo on the front but is physically no different than even the old 6x86 chips.  Manufactured using a 0.35 micron die the M-II generates a considerable amount of heat, however if you are familiar with the older 6x86 (not the 6x86L) chips then you don't have to worry since the heat production of the M-II is no where near that of the first 6x86 processors.   A standard heatsink and fan will suffice, heatsink compound will definitely help if you plan on pushing the processor to its other words, overclocking...

Overclocking & Weaknesses
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