Just added more RAM... DIMM 2 on both risers shows empty?!

Discussion in 'Mac Pro' started by Kingsly, Dec 25, 2008.

  1. Kingsly macrumors 68040


    So I just got an extra 4GB of RAM in two 2GB matched pairs. I intend to get another 4gb for an even 8, but in the meantime 6 gb works.

    The problem is that DIMM 2 on both risers appears to be faulty (haven't bothered to try 3 and 4). The new RAM only shows up if installed in DIMM 1 on each riser, in place of the factory RAM. Additionally, factory RAM does nothing in DIMM 2.

    Are my riser boards faulty? MLB (I sure hope not)?
  2. chromatronic macrumors member

    Nov 25, 2008
    Non, its because mac pro dont take DIMM but FB-DIMM...
    i asked yesterday about that before ordering....
    so your ram will never work in the mac pro...
    you need FB-DIMM
  3. Kingsly thread starter macrumors 68040


    I have FB-DIMM. 800mhz, matched pair, Apple spec.
    Something is up with the riser cards, since my new RAM works in slots 1. See the pic, DIMMs 2 on both risers A and B should show 1gb each of factory RAM.

    FWIW, System Profiler still refers to RAM slots as being DIMMs. It doesn't make the distinction between fully buffered RAM or not. ;)

    Attached Files:

  4. Umbongo macrumors 601


    Sep 14, 2006
    You have it installed incorrectly. This how it should be:

    Riser A slot 1: 2GB
    Riser A slot 2: 2GB

    Riser B slot 1: 1GB
    Riser B slot 2: 1GB

    Basically you fill A:1&2, B:1&2, A:3&4, B:3&4 starting with the largest DIMMS. The exception is if you only have 2 DIMMS they can go in slots 1 on each riser for improved performance and that is why Apple ship them that way. It's all in the manual if you need any more information.
  5. UltraNEO* macrumors 601


    Jun 16, 2007


    Page 46 of your MANUAL..
  6. Kingsly thread starter macrumors 68040


    Aha. If someone would please fill out and mail the correct paperwork to have my intelligence license suspended, that would be greatly appreciated.

    I've done Mac Pro RAM installs (correctly) literally hundreds of times while working both for Apple and for third party repair centres. :rolleyes:
    I have officially become an idiot. :eek:

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