Mac Pro Memory - Info from Intel Data Sheets

Discussion in 'Mac Pro' started by Gonk42, Apr 23, 2009.

  1. Gonk42 macrumors 6502

    Jan 16, 2008
    near Cambridge
    I've been wasting time poking around the Intel data sheets for the 5500 and 3500 series Xeon to find out what the memory limitations really are. This is what I've found (I apologise if it is already common knowledge.)

    The 3500 series is limited to 1066 memory and to unbuffered memory and to
    a maximum of 24GB with a maximum of 2 dimms per channel. This means
    that for the Apple quads 4GB dimms is the limit (16GB). It also explains
    why Apple has specified the memory as unbuffered and 1066.

    The 5500 series will take unbuffered or registered but not both. This
    should mean that the Apple octos could take the (at present) much
    cheaper registered 4GB dimms but unfortunately no one has reported
    trying this out yet. (I can't see why it shouldn't work as the
    memory is connected directly to the processor - I can't see how
    Apple could change this or why they should want to.) The memory
    limit for the 5500 series is much higher so in future I guess 8GB or
    16GB dimms could be used (Samsung have already reported 16GB
    dimms) so for future proofing the octo models have a more
    flexible memory controller.

    The 2.66 and 2.93GHz octos should take the faster 1333 memory
    provided there is only one dimm per channel (ie a total of 6 dimms).

    In summary

    Apple has specified memory that will run on either quads or
    octos presumably to avoid confusing customers and complicated the
    supply/servicing etc.

    Though quads have been shown to go to 16GB this may be their limit
    while the octo models may be able to go much higher.

    It is probable but not yet been demonstrated that the 2.66 and 2.93 octos could take 6x4GB registered 1333 memory.

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