09 Mac Pro Memory Upgrade Question

Discussion in 'Mac Pro' started by Black107, Dec 13, 2010.

  1. Black107 macrumors regular

    Jun 5, 2009
    So ram prices have finally come down and I want to load up my 2009 8-core mac pro.

    It currently has 6x1GB, with 3 sticks in each riser.

    I've been browsing different configurations on OWC and am sort of confused how some of them work.

    One configuration, for example is 3x4GB for 12GB total. Since this setup is only 3 sticks, if I removed all of the sticks currently in the computer and put all three of those in one of the risers and left the other riser empty, will the machine run?

    If I did purchase this setup, could I put the 3x4GB sticks in one riser, put one of the existing 1GB sticks in the 4th slot on that riser, and then fill the second riser with 4 of the 1GB sticks? I know there are differences between triple/dual channel, but I haven't seen whether the stick configuration in the two risers has to be identical...

  2. nanofrog macrumors G4

    May 6, 2008


    Neither configuration is ideal (not balanced in terms of capacity), but they will work. For further clarification as to how/where you should place the DIMM's, take a look at the DIMM Replacement instructions (page 4).
  3. Black107 thread starter macrumors regular

    Jun 5, 2009
    Thanks! Why do you say having just 3x4GB isn't ideal when the doc you referenced said if you have 3 dimms do slots 1,2,3 (leaving the second riser empty)?

    Would it be better to buy 3x4GB, install 1x4GB in slots 1, 2, 5 and 6. Then install 1x1GB in slots 3, 4, 7, and 8? Would I notice a speed drop if I put in the 1GB sticks vs running just 4GB sticks?

  4. nanofrog macrumors G4

    May 6, 2008
    You only have RAM on a single memory controller. So for the second CPU to get access, everything has to be passed over the QPI interface between the CPU's.

    The kit only has 3x DIMM's in it. So it would be impossible to make it work in 4x slots.

    Unless you already have another 4GB stick on hand or will purchase it (buy 4x 4GB Sticks).

    Now there's another note you need to be aware of if the memory is being bought from OWC; their 4GB sticks don't mix with the OEM memory, so you'd want to make sure they're all on one CPU, the OEM on another (1GB sticks, as you seem to be interested in doing). This keeps them on separate memory controllers (one in each CPU).
  5. degl macrumors member


    Jun 12, 2010
    I have the same 2009 2.26Ghz 8-core MacPro, and buy this 215$ Crucial Memory kit
    Put each 4GB stick on socket 1 of each memory modules and now have 14GB of Ram, 15 days no problem at all and making a full 13 episode animated series in after effects and Premiere Pro, no hangs!!

  6. Black107 thread starter macrumors regular

    Jun 5, 2009
    Doh, yep I meant 4x4gb. Sounds like running the singles in addition to the 4's isnt ideal and apparently not possible with owc ram. I guess I'll just get 4x4 and call it a day. Unless running 6x2 would some how make it faster because it's using triple channels instead of double with 4x4?
  7. nanofrog macrumors G4

    May 6, 2008
    Triple channel is useless to most people, as their software can't take advantage of it (doesn't work in a manner that will utilize the additional bandwidth). Which is why capacity tends to trump memory bandwidth for most users.

    The exceptions would be things like scientific/engineering simulations for workstation use.

    But application suites such as CS5 or similar, do not fall into this holy grail of software. Fill the slots if you need to for capacity reasons, and be done with it. ;) :p

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