L2 memory cache - what difference does it make?

Discussion in 'MacBook Pro' started by tomtinfoiled, Jun 10, 2008.

  1. tomtinfoiled macrumors newbie

    Joined:
    Jun 10, 2008
    #1
    hello. after being a bit disappointed with the MBP no show at WWDC i'm getting ready to order the current model, as i badly need it for some gigs with my band.

    could someone please explain what this means

    "2.4GHz Intel Core 2 Duo processor with 3MB on-chip shared L2 cache running 1:1 with processor speed; or 2.5GHz or 2.6GHz Intel Core 2 Duo processor with 6MB L2 cache"

    am i going to get a significant boost with the 2.5 6mb?

    also, would the 2.4ghz MBP run faster than the 2.4ghz top end MacBook? that's been irritating me for a while now!

    thanks for your help!

    tom
     
  2. alphaod macrumors Core

    alphaod

    Joined:
    Feb 9, 2008
    Location:
    NYC
    #2
    It doesn't make a lot difference; the analogy of cache is a bit hard to explain, but more is better, but there are always other factors that affect total performance.

    And the 2.4 in the MBP should run almost exactly the same as the MB 2.4; they are the same processors.
     
  3. CWallace macrumors 603

    CWallace

    Joined:
    Aug 17, 2007
    Location:
    Seattle, WA
    #3
    The main advantage of cache is it is significantly faster to access then main memory. So the more cache you have, the more data it can store and the less often the CPU has to access main memory. However, it's not a "night and day" difference increasing the cache. Plus the cache generates heat and draws power so the more of it you have, the greater the impact on battery life as well as performance.

    So I view it as a "nice have", but not a "must have". I bought a 2.4GHz because the money saved over the faster models paid for more main memory (it may be slower then cache, but it is faster then the HDD :D ), a larger HDD, and AppleCare.
     
  4. alphaod macrumors Core

    alphaod

    Joined:
    Feb 9, 2008
    Location:
    NYC
    #4
    Here's a good analogy of what cache is by Scott Mueller.

    (Sorry for the crappy quality; used a camera because scanning a 1600 page book is kind of too bulky to handle)

    [​IMG]

    For L2 cache the explanation is the same except another "cart" that's bigger, but a bit further away than L1, but still faster than memory.

    And yes the book is kind of old hence the mention of a Pentium II
     
  5. tomtinfoiled thread starter macrumors newbie

    Joined:
    Jun 10, 2008
    #5
    nice one.

    i'm not too sure if i understand exactly what the cache does but i fancy a hamburger!

    i'm going to order the 2.4ghz MBP pretty soon.

    thanks for your help.
     
  6. alphaod macrumors Core

    alphaod

    Joined:
    Feb 9, 2008
    Location:
    NYC
    #6
    It's memory close of a smaller size that's closer and faster than RAM; cache controller guesses what the CPU needs next; if it's guesses correctly (90% success), there are no slowdowns; if it guesses incorrectly (10% "cache miss"), data must be retrieved from RAM/HDD. The bigger cache, the less likely the guesses can fail, so therefore less slowdowns.
     

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