Re: Amount of RAM L1 cache on a processor will support
dman <dsh8290@rit.edu> writes:
> On Tue, Dec 11, 2001 at 01:17:30PM -0500, David Teague wrote:
> |
> |
> | If you put more RAM in a computer system than the caching system
> | will suppport, the system will run more slowly than it would with
> | less RAM. IF I understand correctly, the amount of RAM depends on
> | the amount of tag RAM.
> |
> | I have 512 MB on my Abit MoBo with a 1GHz Athlon.
> |
> | How do I determine how much RAM the L1 cache in a 1GHz Athlon will
> | support?
>
> According to
> http://www.amd.com/us-en/Processors/ProductInformation/
> 0,,30_118_756_759%5E1151,00.html
>
> (all on one line)
>
> Cache Architecture: The AMD Athlon processor boasts a 384K total
> full-speed on-chip system cache including 128K L1 cache--four
> times that of Intel's Pentium III processor--and 256K on-chip
> full-speed L2 cache.
>
>
> There is no limit on the amount of system RAM based on processor
> cache. Certainly when you have many cache misses, you lose
> performance, but the whole purpose of cache is to try and guess which
> memory you will need next (through some hueristic algorithms) so that
> you have a cache hit and don't have to go all the way out to that very
> (relatively!) slow memory.
Umm, not quite. There can be a limit on the amount of RAM that can be
cached based on the processor, but more common is a limit based on the
chipset, which I believe is what David was basing his question
on. Namely the 430(FX|VX|TX|HX) chipsets were, generally, limited to
caching 64MB of RAM. Even given the chipset you can't automatically
say what amount of RAM it could cache. A quick google search pulled up
the following that may be of interest:
http://www.makeitsimple.com/articles/ramguide/ramguidep6.htm
http://www.stud.fernuni-hagen.de/q3998142/pcchips/howto/cache.html
http://www.tomshardware.com/site/faq.html
Of course, David was asking about an Athlon system. As far as I know
neither the latest PIV or the Athlon boards/CPUs have a limit on the
amount of RAM that can be cached. At least to the limit of RAM the
particular board supports.
Gary
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