Mac Pro 5,1 RAM question

Discussion in 'Mac Pro' started by w8ing4intelmacs, Jun 16, 2015.

  1. w8ing4intelmacs macrumors 6502a

    Feb 22, 2006
    East Coast, US
    I have a Mac Pro 5,1 2.8 single with 16GB (4x4GB).

    I got a great price on a 16GB stick but it wasn't playing nice with the other memory. After doing research, I guess I got a 16GB RDIMM and my other memory are UDIMMs. So much for my cheap way of upgrading to 28GB.

    So, do I keep the one stick of 16GB and sell the 4x4GB? There's the part of me that's afraid that RDIMMs are harder to come by and that even if I do buy more RDIMMs, they still won't play nice together.

    Also, how can you tell if it's an RDIMM or UDIMM if it has a heatspreader covering it?
  2. DeltaMac macrumors G3


    Jul 30, 2003
    All 16 GB sticks will be RDIMMs - don't think you will find UDIMM 16GB
    You can't mix UDIMM and RDIMM
    Some other info here, mostly about some other choices.
  3. js2704 macrumors member

    May 20, 2015
    If you got a good deal on the 16GB I'd sell it and pick up ex-server RAM on eBay - 8GB sticks are pretty reasonable and would play fine with the stock 4GBs so you could go from 12-24-32 incrementally
  4. iBuildMacs macrumors member


    Dec 29, 2014
  5. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    ??? The Apple stock RAM is UDIMM, and all the manual clearly state that use UDIMM? Why stay away from it?
  6. iBuildMacs macrumors member


    Dec 29, 2014
    Original Apple RAM is ECC. It usually ends in E. UDIMM ends in U.

    U - unregistered or unbuffered
    E - ECC (error correcting code)
    R - registered

    There is ECC and non-ECC registered RAM. The same with unregistered; some are ECC, some not.

    I recommend getting E or R. I have worked on thousands of Macs. Apple never ships with UDIMM. They always ship with ECC on the Mac Pros... or R in the case of 16GB modules.
  7. stjames70 macrumors member

    Jul 5, 2009
    The official RAM for the 5,1 is Unregistered ECC RAM.

    It is costlier and harder to find than Registered ECC RAM.

    Buy all your RAM from one manufacturer and one source if you can help it -- it avoids compatibility problems.

    My 5,1 runs 64GB of Registered Hynix DDR3 ECC 1333 MHz RAM. Do a search for it. Prices are reasonable.
  8. h9826790, Jun 29, 2015
    Last edited: Jun 29, 2015

    h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    Please check the manual before you "assume" the answer is right. The following is copied from the 4,1 Apple tech guide. AFAIK, the 5,1 still use the same type of RAM, just a bit faster.

    Mac Pro (Early 2009) comes with a minimum of 3 GB of memory, installed as three 1 GB unbuffered dual inline memory modules (UDIMMs).

    DIMMs must fit these specifications:

    • PC3-8500,1066 MHz, DDR3 SDRAM UDIMMs

    • 72-bit wide, 240-pin modules

    • 18 memory ICs maximum per UDIMM

    • Error-correcting code (ECC)

    Anyway, I think only the new Mac Pro may come with the RDIMM (4x16G), and all old Mac Pro comes with UDIMM (stock max 8x8G, all UDIMM) .
  9. 666sheep macrumors 68040


    Dec 7, 2009

    Haha, "E" e.g. in "PC3-10600E" stands for ECC UDIMM.
  10. lowendlinux Contributor


    Sep 24, 2014
    North Country (way upstate NY)
    He builds Mac's ;)
  11. ActionableMango macrumors G3


    Sep 21, 2010
    ECC and UDIMM are not mutually exclusive. My 2010 Mac Pro shipped with UDIMMs that support ECC.

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