Question about 1333MHz ram in Mac Pro 5,1

Discussion in 'Mac Pro' started by w8ing4intelmacs, Jul 13, 2015.

  1. w8ing4intelmacs macrumors 6502a

    Joined:
    Feb 22, 2006
    Location:
    East Coast, US
    #1
    I upgraded the CPU on my Mac Pro to a X5680 (Westmere 3.33 Hexcore).

    My two 8GB sticks run at 1333MHz fine, but my 16GB stick only runs at 1066MHz (all are RDIMMs). I've tried it with all three sticks installed and with the 16GB only. I've also tried the 16GB stick in each slot. In the first three slots, it ran at 1066MHz. But interestingly enough, the 16GB installed in the 4th slot wouldn't even start up (blinking power light).

    I've been assured that the memory is 1333MHz. Just wondering if I'm doing something wrong or missing something.

    Part number: Black Diamond M-1333TER-16384BD26.

    (they all ran at 1066MHz with the original Nehalem W3530)
     
  2. Inutopia macrumors 6502

    Inutopia

    Joined:
    Apr 8, 2009
    Location:
    South of Heaven
    #2
    You need to reset PRAM after a CPU swap for the faster RAM to work at the faster speed, at least that's what I found.
     
  3. w8ing4intelmacs thread starter macrumors 6502a

    Joined:
    Feb 22, 2006
    Location:
    East Coast, US
    #3
    I tried resetting the PRAM and the SMC. The 8GB sticks work fine. Still seeing 1066 on the 16GB stick.
     
  4. w8ing4intelmacs thread starter macrumors 6502a

    Joined:
    Feb 22, 2006
    Location:
    East Coast, US
    #4
    Ok. So, I tried the two 8GB sticks and a different 16GB stick, all of which run at 1333MHz. But this one particular 16GB stick runs at 1066MHz.
     
  5. Inutopia macrumors 6502

    Inutopia

    Joined:
    Apr 8, 2009
    Location:
    South of Heaven
  6. flowrider macrumors 601

    flowrider

    Joined:
    Nov 23, 2012
    #6
    Not interesting at all. All the CPUs in a 4,1 or 5,1 Mac Pro are three channel. The third channel uses RAM populated in slots 3 and 4. Slots 3 and 4 are interconnected and if you only populate slot 4, you get NADA!

    Lou
     

Share This Page