herd that installing memory in mac pro in sets of 3 works best is this true

Discussion in 'Mac Pro' started by rangerfreak1, Mar 28, 2009.

  1. rangerfreak1 macrumors member

    Oct 29, 2008
    i was reading an article online and it said that installing memory in the mac pro should be done in sets of 3 or elses there will be a memory slow down.is this true
  2. cmaier macrumors G5

    Jul 25, 2007
    Yes and no. For a given quantity of RAM, threes is better than twos.

    However, a lot of people take this to mean they should leave slots empty - probably not. The penalty of having insufficient RAM (and thus having to page to disk) is far higher than the penalty for dropping down to single channel for the last DIMM.
  3. jmpage2 macrumors 68040


    Sep 14, 2007
    It depends on the bus architecture. Double memory bus support become common several years ago and you got better performance if you ran memory in matched pairs.

    The new buses in the Nehalem boxes uses a triple memory bus, so generally you would get better performance with the memory in a matched triple pair, which is why they are sold configured this way with 3X1 GB or 3X2 GB.

    The good news is that apparently you can run the quad MP with 4GB DIMMs so you should be able to run 4X3GB and get very good performance and have 12GB of memory.
  4. Boneoh macrumors 6502


    Feb 27, 2009
    So. Cal.
    I ran benchmarks on my 09 MP 2.26 octo before and after adding the new memory.

    The test were run using diglloydTools Stress Test v 1.1.0 64 bit.

    With 12 gb, 6 x 2 gb the max memory speed was 10,421 MB/sec.
    With 16 gb, 8 x 2 gb the max memory speed was 9,024 MB/sec.

    There is a slight performance penalty, but as cmaier has pointed out, the penalty is greatly offset if you have to page to hard disk. Also, OS X does a good job of caching applications in your memory.

    You mileage may vary! :)
  5. rangerfreak1 thread starter macrumors member

    Oct 29, 2008

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