Windows XP and the L2 cache fix issue/confusion

Question

Hi, I've had several Dell computers over the years and in fact I've just bought another one, a Dimension 8300 3.0Ghz (HT). The setup screen reports that this processor has 1024 of L2 cache.  I haven't seen much written about this on the Dell forums so I thought I'd ask. Windows (all NT,2K, XP versions) is set up to recognise only 256k of L2 cache by default.  So if your processor has more than that (as a lot of the newer ones do) you are presumably not taking advantage of the processors increased L2 cache. I was the sysadmin for a company and we had a quad processor (Xeon PII) Dell 6300 that had 1024 L2 cache on each processor and I remember how slowly it ran until I adjusted the L2 cache size in the Windows registry to match what the processors actually had. The question is this: I just got my new machine and haven't adjusted the Windows L2 cache setting (it was setup only last week and has only what the factory installed on it).  Is there still a need to go in and adjust the L2 cache size in the registry to match the L2 cache size of the processor or is this automatically handled by the operating system in some other way? Secondly, if I do need to adjust the L2 cache size in the registry, why isn't this done by the factory when they image the machine?  Is this some undocumented tweak that Dell doesn't know about, or doesn't support, or is actually bogus/bad information? Thirdly, (if this is a valid tweak) since the processor is a hyper-threaded 3.0 Ghz, do I set it to 512kb (half for each of the 'processors' in the chip) or set it to 1024kb? Here's a link to the site that I'm referencing: http://www.winguides.com/registry/display.php/116/  Thanks, Mike

msgale · Answer

From the link you supplied, 'This tweak is only useful for older processors with the cache located external to the CPU.'   Note the word EXTERNAL, all internal caches  L1, L2, and L3, if you have it are managed by the CPU.  Hyperthreading is not dual core as are the Power PC G5 chips from IBM.  As a follow up I check two of my PCs a PWS 530 Dual 1.7 Xeon Processors 256kb cache each and a PE1600SC dual 2.0 Xeon processors 512 kb cache.  In the registry entry the size was zero, which is what I expected since none of the caches are external.   Message Edited by msgale on 08-29-2004 01:08 PM Message Edited by msgale on 08-29-2004 01:21 PM

WonderingAloud · Answer

Right!  Good catch.  I must have missed that! Thanks, Mike

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