Can i mix memory size ?

Discussion in 'Mac Pro' started by enny001, Jul 25, 2015.

  1. enny001 macrumors member

    Joined:
    Apr 30, 2013
    #1
    Hi guys i have mac pro 2009 2.66 and have 12x3 gb owc with one free slot can add another 8 gb in to that free slot or it hsas to match i was told by own it has to match

    Thanks
     
  2. T5BRICK macrumors 604

    T5BRICK

    Joined:
    Aug 3, 2006
    Location:
    Oregon
    #2
    *edit* disregard my answer. I accidentally clicked on the Mac Pro section, I was thinking MacBook Pro.

    To answer the question in the subject line. Yes you can mix different sizes of memory.
     
  3. enny001 thread starter macrumors member

    Joined:
    Apr 30, 2013
    #3
    why was i told by owc that i cant they toled me that it has to be 4 gb all of them. Will i get any problems if i place another 8 gb with 3 sticks 4 gb i will have 20gb if i do this

    Thanks
     
  4. Studio K macrumors 6502

    Studio K

    Joined:
    Feb 17, 2013
    Location:
    United States
    #4
    Try placing the largest memory module into Slot 1. 8GB in slot 1 and 4GB in slots 2,3, & 4. The worst thing that can happen is the Mac Pro won't boot. If it does start up, then OS X will notify you if the memory is installed in the correct confiuration.

    I'm using 4GB modules in slots 1 & 2 with 2GB modules in slots 3 & 4.
     
  5. flowrider macrumors 601

    flowrider

    Joined:
    Nov 23, 2012
    #5
    RAM 2009.jpg Placement matters. Following the Apple guide here: BTW, OWC is wrong as usual!

    Lou
     
  6. Draeconis macrumors 6502a

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    May 6, 2008
    #6
    You can't do that, no. 8Gb DIMMs can't be mixed with smaller modules, the Mac Pro won't pass POST if you try.
     
  7. h9826790 macrumors 604

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #7
    We can, I did that already. It's about the spec, but not the size (e.g. we can't mix RDIMM with UDIMM).
     
  8. Draeconis macrumors 6502a

    Joined:
    May 6, 2008
    #8
    You can't, because I've tried exactly this and it doesn't work.

    8Gb and 16Gb modules can't be mixed with 1, 2 and 4Gb.
     
  9. h9826790, Jul 27, 2015
    Last edited: Jul 27, 2015

    h9826790 macrumors 604

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #9
    Done! Case closed.

    I can mix 8G with 2G sticks, ECC RAM with non ECC RAM, and 1333 with 1066 RAM.

    The result is all RAM works at 1066 without ECC. That's it.

    Screen Shot 2015-07-27 at 18.16.51.jpg
    Screen Shot 2015-07-27 at 18.17.12.jpg
    Screen Shot 2015-07-27 at 18.17.25.jpg
     
  10. IowaLynn macrumors 6502a

    IowaLynn

    Joined:
    Feb 22, 2015
    #10
    In the early days of the 4,1 8GB DIMMs could not (and they were not available even to use or test in early 2009) - but that changed in the year afterwards, maybe by the time the Mid-2010 came out.
     
  11. ActionableMango macrumors 604

    ActionableMango

    Joined:
    Sep 21, 2010
    #11
    Troublemaker!
     
  12. Draeconis macrumors 6502a

    Joined:
    May 6, 2008
    #12
    Huh. Didn't know that. I wonder if it's because my 8Gb and 2Gb DIMMs are both ECC.
     
  13. h9826790 macrumors 604

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #13
    Are they all UDIMM? The biggest restriction AFAIK is you can't mix RDIMM with UDIMM.

    Anyway, there is no guarantee mix RAM can work flawlessly. All I can prove is just that's possible.
     

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