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Subject: Re: Importance of L2 cache speed/size for diff programs (was:..Genius speed?

Author: Tom Kerrigan

Date: 10:55:01 08/12/98

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On August 12, 1998 at 10:44:40, fca wrote:

>You wrote:
>"Aside from software differences, the Pentium MMX/200 has a 66MHz L2 cache
>(possibly smaller than 512k) whereas the Pentium II/300 has a 512k 150MHz L2
>cache. If a program really bangs on the L2 cache, it will go much faster on the
>Pentium II."
>But since the core (P2/300 vs P200MMX) is so much faster, the extra/faster cache
>(even if accessed a lot) simply serves to alleviate what the faster core would
>*otherwise* have made into a bottleneck.  L2-hit rates etc suggest in itself
>this would not be able to increase the speed ratio above that the cores deliver.

Sort of. Notice that the 200/66 core clock speed/L2 cache speed ratio is much
less than the 300/150 ratio, so if L2 cache is a bottleneck on the Pentium
MMX/200, then it's less of a bottleneck on the Pentium II/300.

>So, I am still surprised at the 2.5x reported.  Aren't you?

Not really. Consider this:

Pentium MMX/200 = 1
Pentium MMX/300 = 1.5 (assume linear scaling)
Pentium MMX/300 * 1.66 = 2.5 (66% improvement from P5 -> P6 core)

So it's not out of the question.

-Tom



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