Any memory configuration ok in current Mac Pros?

Discussion in 'Mac Pro' started by powerbook911, Dec 19, 2009.

  1. powerbook911 macrumors 68040


    Mar 15, 2005
    The current entry-level Mac Pro includes 3 GB of memory. 3 sicks of 1 GB.

    Can I had 1 stick of 2 GB to that, to get 5GB and it does not hurt system performance? There is no dual channel nonsense to worry about? Put in any configuration you want?

  2. Umbongo macrumors 601


    Sep 14, 2006
    4 DIMMs have around 70% of the bandwidth 3 can achieve, but you likely won't notice it in real world performance. Yes you can mix capacities and do what you propose.
  3. nanofrog macrumors G4

    May 6, 2008

    And the additional memory gained by doing this will actually benefit the user (assuming the RAM capacity isn't more than what's needed; i.e. over-kill, which is hard to do at a reasonable cost with the '09's, and more so on the Quads). :)
  4. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    The memory is configured in three channels, with an extra DIMM slot for channel 1. When running DIMMS in all four slots, memory performance is impacted. It's ideal to run just three DIMMS for full tri-channel performance. If you can afford it, it would be ideal to replace the 3x1 with 3x2GB for 6GB of tri-channel RAM.

    Check out the RAM upgrades at OWC... they have good prices on memory upgrades and will even buy-back your old sticks I think.
  5. nanofrog macrumors G4

    May 6, 2008
    If your current software can run triple channel, then yes. But as most applications can't come close, the additional memory would make more sense.

    I'd expect this to change eventually, once software catches up. But the question is when. A few newer system generations may be out by then. ;)
  6. powerbook911 thread starter macrumors 68040


    Mar 15, 2005
    Thanks guys. I figured there was a reason it only came with 3GB.

    If I get the machine, I may just run 3 GB for a month, and then go to 6GB.

    I'm not a super pro user and only considering this because the iMacs have so many problems.

    Thanks for clarifying what I need to do on the RAM. I think it will be a fun moment to open up the Mac Pro! Plus, knowing I can add plenty of storage and change graphic card when I want!
  7. powerbook911 thread starter macrumors 68040


    Mar 15, 2005
    I'm sorry to bug you guys again.

    For the 3 slots that are best to use, they don't have to match and you still get the full benefit of only running 3 slots? Like a 2x1x1 configuration for a couple months doesn't slow it down? Or if I buy a 4GB after that a 2x4x1 is ok too, if you only use 3 slots?
  8. gugucom macrumors 68020


    May 21, 2009
    Munich, Germany
    First of all you need to make sure you use only UDIMMs or RDIMMs. You cannot mix the two sorts. The lower capacities tend to come in UDIMM which was originally fit to your Mac Pro. So if you want to continue using them stick to UDIMM. If you consider 4 GB DIMMs you better look at RDIMMs.

    Regarding the mixing of different capacities you should try to keep the three channels populated equally for maximum bandwidth. If that hurts your capacity you can deviate but you should stay as closed to balanced as possible.

    Your four slots are connected to the three channels in such a way that the first two slots serve one channel each. The last two slots serve only one channel. So a good way of deviating would be to fit 2 GB modules in the first two slots and 1 GB modules into slots three and four. That way you get 6 GB, have all channels with the same capacity and get to use some of your 1 GB modules.

    This is actually the way I run may octad at the moment. Octads have the same structure as quads only that they have a second memory bank which works exactly the same way.

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