XP L2 Cache Setting for Quad Core CPU

Microsoft Windows xp home edition with s...
September 24, 2010 at 08:19:07
Specs: Windows XP, Intel Quad Core Extreme QX9650 w/ 4MB PC-9600 DDR2 @ 1200MHz

I've read the posts about the L2 cache setting in the XP registry. I can get to it and I can change it, so that's not my question. My question is: what should I set it to if I have a Quad Core CPU where half the cache is shared by two cores? The listed L2 cache size is 12MB but I read that with these chips the cache is split in half because it's not a true Quad Core but rather two Dual Cores spliced together. So I figured if each core only sees 6MB then I should set the XP L2 cache setting to 6MB, but I'm not positive.

So, should it be 6MB or 12MB?


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September 24, 2010 at 09:07:22
Set the Level 2 cache setting to zero. Windows will auto-detect the correct value. Note that Windows will not update the registry to the detected value.

Also note that this setting has been seriously misrepresented in the many "tweaking guides" found all over the internet. The setting was meant for very old CPU's that did not permit auto-detection of the correct value. For the vast majority of modern CPUs it is of no value.

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September 24, 2010 at 10:03:03
Mine was 0 so I figured I should set it manually. I set it to 6MB and I think I saw an improvement in speed. If it's 0 what does that mean? I saw posts that said XP won't recognize newer CPUs, that's wrong?

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September 24, 2010 at 10:33:07
Zero is the default value, meaning that Windows is to detect the correct value. Many registry values work this way. Many people think that Windows did not detect the value because the registry was not updated. Windows sets this value to zero during installation ant it will NEVER set it again, regardless if the correct value is detected or not. I don't know of any utility, aside from a kernel debugger, that will determine if the value has been detected.

Windows asks the CPU for the correct value so I see no reason why this would fail, aside from old CPUs (original Pentium) that did not have this feature.

According to Microsoft the performance penalty for getting this value wrong is about 2% maximum and usually less.

I see no reason to set this value to anything but zero.

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September 24, 2010 at 10:57:13
Ok thanks for the info. I originally got curious about this setting when 3DMark 06 system info showed my L2 at 0B. However, even after the registry change, 3DMark still said 0B. I'll just go back to 0 then.

Thanks again!

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