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 G3

    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 603

    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

    Joined:
    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 G4

    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: Nov 19, 2018

    h9826790 macrumors G4

    h9826790

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

    I can mix 8G with 2G sticks, and ECC RAM with non ECC RAM, and 1333 with 1066 RAM, and in the non optimum order / slots.

    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 65816

    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 G3

    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 G4

    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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