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New 15"/17" AlBooks -- no L3 cache? - Mac Portable

Do my eyes deceive me, or is there no more L3 cache in the 15" and 17" Aluminum Powerbooks? There is, however, 512K of L2. There was never any L3 in the 12". I'm guessing that the new processor behaves a little differently from the older iteration, but I still wonder why the L3 has been taken out. Does the 7457 not need L3? Does doubling the L2 make up for the lack of L3?...

  1. #1

    Default New 15"/17" AlBooks -- no L3 cache?

    Do my eyes deceive me, or is there no more L3 cache in the 15" and 17"
    Aluminum Powerbooks? There is, however, 512K of L2.

    There was never any L3 in the 12".

    I'm guessing that the new processor behaves a little differently from the
    older iteration, but I still wonder why the L3 has been taken out. Does
    the 7457 not need L3? Does doubling the L2 make up for the lack of L3?
    Kevin Guest

  2. #2

    Default Re: New 15"/17" AlBooks -- no L3 cache?

    In article <bk756q$8p1$ccs.carleton.ca>,
    Kevin <com> wrote: 

    L3 cache is expensive, and as I pointed out in an earlier message, for
    the vast majority of GUI code, it doesn't help much. That's why no desktop
    PC's have L3 cache at all - the PIII and PIV just have a smallish L2
    cache like the G4 in the new powerbooks. Only serious server chips tend
    to have big L2 or L3 caches (Pentium Xeon, POWER4, Alpha, Itanium2, for
    example).

    In G5 and Opteron machines, HyperTransport makes it a moot point ; main
    memory bandwidth and latency on hypertransport is so good that cache is
    less important. We have an Opteron box and man, is it fast. Roughly
    twice the speed of a 2.8 GHz Pentium IV Xeon, on our code.

    Tim

    Tim Guest

  3. #3

    Default Re: New 15"/17" AlBooks -- no L3 cache?

    In article <bk756q$8p1$ccs.carleton.ca>,
    Kevin <com> wrote:
     

    Haven't they also increased the main memory speeds on the 15" models? A
    larger L2 and faster main memory access might be the difference here.

    Bob Harris
    Bob Guest

  4. #4

    Default Re: New 15"/17" AlBooks -- no L3 cache?

    Bob Harris <dec.com> wrote: [/ref]
     

    Ah, true. Thanks guys, that helps.

    I guess my next question is, does this mean the 12" is now up to par (or
    closer to it) with the 15" and 17"? With the previous models, the 12"
    lacked the 1 MB of L3 cache that the other two models had, and people said
    it made a noticable difference. Will a 1 GHz 12" now equal the performance
    of the new 1 GHz 15", for example?

    Thanks guys :)

    Kevin Guest

  5. #5

    Default Re: New 15"/17" AlBooks -- no L3 cache?

    In article <bk756q$8p1$ccs.carleton.ca>,
    Kevin <com> wrote:
     

    For these machines, yes.

    L3 cache is useful only in certain cirstances: when you're
    accessing a large amount of memory repeatedly, but not so large
    that it won't fit in the cache. So most computers with L3
    aren't getting much advantage from it most of the time unless
    they hit that magic sweet-spot of loading that precise number
    of bytes repeatedly.

    Under most cirstances doubling the L2 cache will be far
    better: it's faster memory, for a start which makes it more
    worthwhile to cache things in it. It doesn't require the extra
    level of protocols to fetch and put so that saves even more
    time. And it doesn't use up as much space on the motherboard.


    Simon Guest

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