cMP RAM Matched Sets

Discussion in 'Mac Pro' started by Bollockser, Jun 12, 2017.

  1. Bollockser macrumors regular

    Oct 28, 2014
    Hi I have a 2x2.26 Quad 2009 Mac Pro 4,1>5,1

    My question is, if I purchase 48GB now (16x3), a matched set of 3, can I later on buy another 48GB matched set of 3 to install in the other processor tray, and retain all the benefits of matched sets (and tri-channel)?

  2. AidenShaw macrumors P6


    Feb 8, 2003
    The Peninsula
    It's pretty much a myth today that "matched sets" of DIMMs are needed or useful. It's a marketing ploy for memory manufacturers to pull three DIMMs out of the box and sell them for more $ than pulling three DIMMs out of the same box and selling them as three separate items. (Normally there's a quantity discount - but "matched set" creates a quantity premium.)

    Of course, having identical or very similar specs for DIMMs on a channel can be useful - but it doesn't matter if you put a Hynix and a Crucial and a Samsung on the same channel if the specs match.

    Systems today are pretty good at dealing with memory DIMM mismatches. They'll look at the DIMMs on a channel and figure out the maximum performance that all DIMMs can hit, and downclock the faster DIMMs to the capability of the slower DIMMs.

    There are some odd issues (like the cMP having 8 DIMMs in a tri-channel setup), but in general it's far, far better to have DIMMs in a sub-optimal configuration than to have memory pressure causes hard paging to the pagefile.
  3. Bollockser thread starter macrumors regular

    Oct 28, 2014
    OK very good. I just dont want to drop the $530 in one lump sum.
    So, 48GB twice it is!
    Thank you.
  4. orph macrumors 6502a

    Dec 12, 2005
    iv never had a problem with mixed ram, and most pleases you can return if needed

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