[RC5] Strange Keyrates

dan carter motion at es.co.nz
Fri Jun 19 20:09:36 EDT 1998

On Thu, 18 Jun 1998 13:02:11 -0700 (PDT), Keith Woodworth wrote:

>Whats the PR for? I have a 166+ and its a PR but have never 
thought much 
>about it till I just saw your post about it.

PR is a controversal rating that means equivalent pentium 
performance. Eg a Cyrix 6x86 PR150 is equivalent to pentium at a 
150 MHz clock rate (even though the 6x86 is only running at say 

PR stands for performance rating, a PR2 rating means equivalent to 
a pentium2. Eg my K6-200 is PR2-200, so it is much faster than a 
pentium-200 and would be equivalent to a pentiumII-200 if such a 
thing existed.

As you may know, Mhz is only a good performance rating if the chips 
being compared are otherwise identical.

In the case of the K5/K6/6x86 etc they are very different to the 

So some lab runs a bunch of benchmarks on all the pentiums. Cyrix 
etc send their chip to that lab and they benchmark it. They then 
look for the pentium with the same benchmark results to decide what 
PR rating the Cyrix chip gets.

Note that the benchmarks run are primarily 'business oriented' 
benchmarks. They do not heavily stress the FPU and they do not use 
Quake FPS as part of the benchmark. Hence while a Cyrix 6x86 PR150+ 
may be slightly faster than a pentium 150 at business apps in 
general, it's equivalent performance in any one application may 
vary. (It is slower at quake).

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