P-rating is part of a long-standing and generally successful attempt by the computer industry to completely befuddle users. Until 1995, all CPUs were rated by their nominal clock frequencies in MHz. A 386DX33 indicates a 33MHz 386DX. Non-Intel CPUs were either clones or less capable variations such as Cyrix's 486DLC. However with the release of NexGen's Nx586 intel's competitors started putting CPUs into the market that outperformed the analogous Intel CPUs in some respects. NexGen solved the problem of MHz implying less than actual performance by substituting the MHz rating of a Pentium that had roughly the same performance their CPU using a somewhat arbitrary scaling factor.

In 1996, Cyrix released a line of 586 and 686 CPUs which outperformed Pentiums of the same clock speed. Cyrix adopted a somewhat less controversial performance rating than NexGen. It is based on the relative performance of their CPU and Intel's Pentium using the PC Magazine Winstone test.

Cyrix 150MHz 6x86 slightly outperforms a Pentium-200 on Winstone and is identified as a Cx6x86-200+. The plus sign indicates that the speed is a P-rating rather than an actual clock rating.

The new ratings are calculated using the comparative performance of the CPU running the Winstone benchmark program. The CPU is given the rating of the Intel Pentium CPU which is just beaten by the CPU being tested.

Last update: spelling 12Oct02

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