RAM slots 4 and 8 stuck at 1066MHz! WHA?

Discussion in 'Mac Pro' started by echoout, Dec 18, 2013.

  1. echoout macrumors 6502a

    Joined:
    Aug 15, 2007
    Location:
    Austin, Texas
    #1
    Hey folks, my pitiful old 2009 5,1 recently got a RAM upgrade from 4 x Corsair XMS3 8GB (1x8GB) DDR3 1333 MHz (PC3 10666) to filling the final 4 slots with more of the same. No matter what order I fill the slots, 4 and 8 show as running at 1066MHz.

    Am I missing something obvious? You see my specs in my signature.
     
  2. Spacedust macrumors 6502a

    Joined:
    May 24, 2009
    Location:
    Poland
    #2
    So 2009 or flashed 4,1 to 5,1 ?

    If flashed 4,1 to 5,1 you won't get 1333 until you replace CPU to 6-core models.
     
  3. flowrider macrumors 601

    flowrider

    Joined:
    Nov 23, 2012
    #3
    Not correct - The faster 4 core CPUs, will handle 1333MHz RAM. All 4 core from the X5550 to W5590 will run at 1333MHz.

    However, I am confused by the OPs statement. Is your RAM showing different speeds for different slots?

    Lou
     
  4. echoout thread starter macrumors 6502a

    Joined:
    Aug 15, 2007
    Location:
    Austin, Texas
    #4
    Like my signature says, flashed to 5,1, using dual 6-core CPUs.

    Slots 4 and 8 are showing as 1066MHz regardless of RAM configuration. All other slots show 1333MHz, regardless of configuration.
     
  5. echoout thread starter macrumors 6502a

    Joined:
    Aug 15, 2007
    Location:
    Austin, Texas
    #5
    Just found this tidbit. Any insight?

    "Dual-processor model

    Slot 1: Memory Channel 1, Processor 1
    Slot 2: Memory Channel 2, Processor 1
    Slots 3 & 4: Memory Channel 3, Processor 1
    Slot 5: Memory Channel 1, Processor 2
    Slot 6: Memory Channel 2, Processor 2
    Slots 7 & 8: Memory Channel 3, Processor 2
    Slots 3 and 4, as well as slots 7 and 8, share a memory channel. The best memory performance is achieved when slot 4 (single-processor model) or slots 4 and 8 (dual-processor model) aren’t occupied. By not populating the second of the paired memory slots, you allow each memory module to connect to its own dedicated memory channel.

    If you do choose to populate the last memory slots, you may reduce optimum memory performance, but only when memory in the shared slots is being accessed."
     
  6. echoout thread starter macrumors 6502a

    Joined:
    Aug 15, 2007
    Location:
    Austin, Texas
    #6
    Okay, I ran Geekbench 3 in 64 bit mode with and without Slots 4 and 8 occupied.

    Slots 4 and 8 empty (48GB):
    Geekbench Overall Multi-Core Score = 30,149
    Memory Multi-Core Score = 4616

    Slots 4 and 8 occupied (64GB):
    Geekbench Overall Multi-Core Score = 30,188
    Memory Multi-Core Score = 4461

    So not a ton of difference either way. Weird.
     
  7. flowrider macrumors 601

    flowrider

    Joined:
    Nov 23, 2012
    #7
    This has been stated in threads before. I leave my slots 4 and 8 MT for this very reason.

    Lou
     
  8. echoout thread starter macrumors 6502a

    Joined:
    Aug 15, 2007
    Location:
    Austin, Texas
    #8
    Couldn't find it anywhere. Thanks.

    I'm just wondering if having those 2 slots full is ever beneficial or detrimental for that matter. Hmm.
     

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