16+4+4+4 Ram on Mac Pro ?

Discussion in 'Mac Pro' started by Macmomomo, May 23, 2015.

  1. Macmomomo macrumors newbie

    Nov 10, 2009
    Its 3*4 gig ram in the Mac Pro 4 core, Can I buy one 16 gig Ram and put in in and get 28 gig total ?

    Or how does that work ?
  2. mattspace macrumors 65816


    Jun 5, 2013
    All the 16s I looked at while researching my upgrade were pretty specific about not playing well with others.
  3. Macmomomo thread starter macrumors newbie

    Nov 10, 2009

    So it wont work? Or what do you mean ?

    How about if I buy the 2*8 and then use the 2*4 gig ? Will that work better ? If even at all ?
  4. omvs macrumors 6502

    May 15, 2011
    At the very least, you shouldn't mix registered and unbuffered DIMMs together. I believe also you can't mix ECC and non-ECC dimms.

    Not sure about mixing different rank dimms together - perhaps that will work as long as they're in different memory channels. Since slot 4 shares with one of the others (not sure if its slot 1 or slot 3), I wouldn't put the odd DIMM in there.
  5. benjaprud, May 23, 2015
    Last edited: May 23, 2015

    benjaprud macrumors member

    Apr 9, 2015
    You can mix ECC and non-ECC although it will work in non-ECC mode. You can't however mix registered and unbuffered memory. High capacity DIMMs are supposed to be quad-ranked (with 36 chips on it for ECC DIMMs) and quad-ranked are supposed to be registered. That said, technology evolves and i'm not aware of every DIMM on the market but be careful about unbuffered/registered.

    Putting a quad-ranked DIMM is likely to clock down the memory at 1066MHz on a 1333MHz capable setup and putting 4 DIMMs will switch from 3-way interleaving to 2-way interleaving with both a small impact on performance. That said the difference in performance is almost unnoticeable and you will benefit more from the increased capacity if you actually use it.
  6. IowaLynn macrumors 65816


    Feb 22, 2015
    Buy two! Then sell the 4's. I am pretty sure all 16's are registered and won't work or play along with non.

    If you will never need more than ~32GB it seems save the trouble and expense and (also sell the 4's) and go 8GB x 4.
  7. deconstruct60 macrumors 604

    Mar 10, 2009
    Pretty sure there were a few 8GB registered DIMMs that were meant to be matched up with 16GB registered DIMMS so should avoid those if keeping the 4GB DIMMS ( which I think all unbuffered; at least for the required tech that matches the Mac Pro 4,1 ). Two unbuffered 8GB is a very low cost, incremental move.

    The other unmentioned issue is whether you eventually want to jump to 6 cores ( and flash to a Mac Pro 5,1 firmware ) which takes a higher spec memory than the four cores. If not really planning on it then don't worry about it, but if on a multi-year upgrade budget process then it is a factor.


    For 32GB it is probably cheaper to go with 4 * 8GB unbuffered.

    Again if 32GB is probably as high as you are ever going to go with this machine then it is a better move.

    If just stopping at 24-32GB because all you can afford now but highly likely going to require 48GB in the future than 2 * 16GB now is a better incremental step.

    If your workload isn't demanding >20GB now and hasn't been on a growth curve for last year or more then preparing for > 32GB probably isn't a good move. If it hasn't been extremely painful memory pressure wise with 12GB ( 3 * 4GB ) shooting for over 32GB probably isn't very well motivated.
  8. Macmomomo thread starter macrumors newbie

    Nov 10, 2009

    I ordered 2x16GB

    Crucial DDR3 1866MHz 16GB DIMM for Mac
    16GB DDR3 1866 MT/s (PC3-14900) CL13 Registered DIMM 240pin for Mac

    I hope this is good enough ?
  9. Draeconis macrumors 6502a

    May 6, 2008
    Basically, no, you can't do that.

    I got some 8Gb DIMMs a while ago, to go from 4x2Gb to 2x8Gb. Tried to use some 2Gb and 8Gb sticks together, and the memory utility greeted me with a message saying you can't mix DIMMs like that.

    From an Apple support page;

    8GB RDIMMs are also supported. The computer will not start if both types of DIMMS are installed in the same computer. For more information, see Mac Pro (Mid 2010): Registered DIMM support.

  10. DanielCoffey macrumors 65816


    Nov 15, 2010
    Edinburgh, UK
    And you won't get 1866 out of the chips either - they will just clock down to the supported speed.
  11. ActionableMango macrumors G3


    Sep 21, 2010
    The best summary I've seen of what works in the Mac Pro and what doesn't, plus performance impacts, was posted here by Benjaprud. He even includes links to supporting documentation.

    It is very useful, but it is too bad it's lost somewhere in middle of a thread instead of being its own post.

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10 May 23, 2015