Triple Channel?

Discussion in 'Mac Pro' started by macman21, Mar 11, 2009.

  1. macman21 macrumors newbie

    Jul 18, 2002
    Call me crazy but are we all assuming the Nehalem Mac Pros can operate in triple channel mode based on the memory configurations suggested by Apple? I can't find anywhere on Apple's site or in the user manual that spells out the ability to run in triple channel mode. I know the integrated memory controller can operate in dual or triple channel mode. Being dual only would explain the number of memory slots. Can any owners of the new Mac Pros confirm triple channel operation? Or has anyone seen it documented one way or another by Apple? I'd love to be wrong...
  2. Tallest Skil macrumors P6

    Tallest Skil

    Aug 13, 2006
    1 Geostationary Tower Plaza
    It can handle any size of DIMM in any combination.

    You can put in one, two, or three matched DIMMs, or no matched DIMMs.
  3. Frozengeek macrumors member

    Mar 9, 2009
    Fairbanks, Ak
    Would be nice to see some Nehalem benchmarks with two, three and four bays filled (or 4, 6, and 8 respectively).
  4. Daim macrumors member

    Jun 16, 2008
    So what will happen if i put in 4x2GB and only 2,5GB or are used in daily work. Will those be accessed in dual channel (slow) or trichannel mode (faster).

    Sounds to me like the 6x1GB version will run faster when less memory (ie 2,5GB) is used because it's accessed in trichannel mode.
  5. Boneoh macrumors 6502


    Feb 27, 2009
    So. Cal.
    I should be getting my 16 gb ram in today.

    I will benchmark first using 12 gb, then try it with 16 gb to see what the deal is.
  6. macman21 thread starter macrumors newbie

    Jul 18, 2002
    Excellent! Thank you.
  7. Daim macrumors member

    Jun 16, 2008
    I really would like to know how Nehalem handles 2x4GB.. like 2xdual channel or 1xtrichannel + 1xsinglechannel?

    I wonder why noone asked this because it's the most important thing when deciding between 6x1 and 4x2GB
  8. JimGoshorn macrumors 6502


    Mar 8, 2009
    Please do report back because that could be an important issue.
  9. Umbongo macrumors 601


    Sep 14, 2006
    Well it depends how you place them. Apple reccomends you go for two dual channel. You get the choice with 8 memory slots on the dual socket Mac Pros.
  10. macman21 thread starter macrumors newbie

    Jul 18, 2002

    It looks like 12GB is better than 16GB, at least under the circumstances of Bare Feats' benchmark. This suggests the Mac Pro is forced into dual channel mode with all slots filled.
  11. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    Intel's own Core i7 motherboard uses the exact same memory configuration as the quad-core Mac Pro. You can read about the details in Section 1.5 of this technical overview...

    There's likely plenty of memory benchmarks available for this board as well (but I don't have time to track them down).


    The way it works is that memory installed in the first three slots (blue slots on the Intel motherboard) run in tri-channel mode with data interleaved across all three DIMMS. If a fourth DIMM is installed, it's obviously accessed in single channel mode since there's no other DIMM's to interleve the data across. However, it doesn't affect the interleaving taking place on the other 3 DIMMs.

    Think of multi-channel interleaved memory as a RAID0 array of hard drives. To carry this analogy to the memory on the quad mac pro, you have three channels in RAID0 with an extra disk on it's own.

    More info here...

    If Apple f'd this up, I'd be very surprised.

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