Re: Amount of RAM L1 cache on a processor will support

[dman <dsh8290@rit.edu>]

On Tue, Dec 11, 2001 at 05:05:24PM -0700, Gary Hennigan wrote:
| 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

| http://www.makeitsimple.com/articles/ramguide/ramguidep6.htm#Cache_RAM_Issues
(added the anchor reference)

Oh, I had never heard of a limit as to _which_ portion of main memory
was capable of being cached before.  I thought he was asking if all
512MB could be cached (simultaneously).  (Hence my response of, "no,
only 384KB can be cached at any given time")

-D

-- 

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