L3 cache

Discussion in 'General Mac Discussion' started by garzy, Feb 3, 2003.

  1. garzy macrumors regular

    Dec 21, 2002
    what does it do? whats the difference from the L2 cache? is there a huge performance boost from one to the other?
  2. Catfish_Man macrumors 68030


    Sep 13, 2001
    Portland, OR
    Different "levels" of cache are basically different speeds. Level 1 cache is very small and very fast, all chips I know of have it. Level 2 cache can be either on chip (fast and small, but slower and bigger than L1) or off chip (larger, but slower), all recent chips I know of have Level 2 cache (almost all have on chip Level 2 cache). Level 3 cache is always off chip (except on Intel's Itanium series), and is just like a larger slower level 2 cache. With a G4+, here's how it works:

    If the program uses 32k or less of data, it's stored in the L1 cache, if not, then the most current pieces of data are. Everything in the L1 cache is in the 256k L2 cache, along with anything slightly less recently used. Even less recently used things are in the 1 or 2 MB L3 cache (which is off chip). If it's not in any of the caches, it has to be fetched from ram, which is really slow.

    Overall, it boosts performance a bit and helps negate the effects of the slow system bus that G4s have.
  3. garzy thread starter macrumors regular

    Dec 21, 2002
    thanks catfish
    youre a wealth of information

    so i guess a level 3 cache would be helpful in applications such as photoshop
    the 12in pb lacks a l3 cache?

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