Wanted: Mac Pro Ram purchase and placement advice

Discussion in 'Mac Pro' started by wizb98y, May 5, 2009.

  1. wizb98y macrumors newbie

    May 4, 2009
    San Diego, CA
    I plan to add memory to a 2008 3.2 Ghz 8-core mac pro that comes
    with standard 2x1GB (2GB) sticks. My original plan is to buy
    2x4GB sticks so that I have a total of 10GB. With this I would
    have to place the memory in two ways:

    Config 1:
    Riser A: 4G 4G XX XX
    Riser B: 1G 1G XX XX

    Config 2:
    Riser A: 4G 4G 1G 1G
    Riser B: XX XX XX XX

    According to the benchmarks at macsales.com
    Memory performance for both config1 & 2 will be bad.
    So what to do. Should I just buy 4x2G sticks instead of
    2x4G sticks to get:

    Config 3:
    Riser A: 2G 2G 1G 1G
    Riser B: 2G 2G XX XX

    for better performance. My preference is to only buy 4G sticks
    and have extra free slots for future memory expansion but is
    concerned with getting poor memory performance in the meantime.
    Recommendations and comments?
  2. -js- macrumors regular


    Jul 30, 2008
    Southern California
    Configuration 1 is what you want. You can't have all four DIMM's only on the top riser. And you are right to only want to buy 4GB DIMM's. It's just the best idea for future memory expansion. And while the highest throughput may be with all 8 slots filled, you increase latency. The magic number of DIMM's is 4, from what I've read on anandtech.

    BUT . . .

    It really doesn't freaking matter. Getting the 4GB highest density FB-DIMM's is far more important. And having enough memory is far more important. A few nano seconds of extra latency is nothing compared with having a page swap to disc.

    FWIW, I bought a 2008 MP with 2x1GB and added 2x4GB, just like you plan to do. I moved one of the 1GB DIMM's down to join the other 1GB DIMM, and then put the 2 4GB DIMM's in slots 1 and 2 of the top riser. OWC has a nice instruction sheet that they provide with their FB-DIMM's.

    10GB is awesome, BTW! You'll love having that much RAM, if your usage patterns are anything like mine.
  3. wizb98y thread starter macrumors newbie

    May 4, 2009
    San Diego, CA
    Thanks for the advise.
    I think you pushed me over to settle on the 4GB sticks.
    Maybe I'll just buy 4x4GB sticks. It is just money :)

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