Will dual 1.25ghz work in a dual 867mhz MDD?

Discussion in 'Mac Pro' started by OrangeSVTguy, Jan 16, 2009.

  1. OrangeSVTguy macrumors 601

    OrangeSVTguy

    Joined:
    Sep 16, 2007
    Location:
    Northeastern Ohio
    #1
    I searched but couldn't find anything that I needed. I picked up some MDDs(dual 1.25 & FW800 1ghz) with bad power supplies and eying up another MDD(Dual 867) which is working. Will the dual 1.25 and single 1ghz processor daughter card work on the previous model? I know the System clock is different and heard about removing a resister on the first gens to 167mhz FSB. I will also try and transplant the PSU too to check to see if my 2 MDDs fully work or not.
     
  2. TimmyDee macrumors member

    Joined:
    Feb 20, 2007
    #2
    Those should work just fine, but the 867 MHz had a 133 MHz bus, whereas the dual 1.0 and above had a 167 MHz bus. Since the processor speed is based off a multiplier of the bus speed, your 1.25 GHz processor will only run at 1.0 GHz on a 867 MHz machine's bus.

    Check out the multipliers here:

    http://www.xlr8yourmac.com/systems/g4_mirrored_drive_doors/G4_MDD_CPU_Module.html

    If you want, you can always play with resoldering the multipliers to achieve higher clock speeds.
     
  3. OrangeSVTguy thread starter macrumors 601

    OrangeSVTguy

    Joined:
    Sep 16, 2007
    Location:
    Northeastern Ohio
    #3
    OK thanks!
    Yeah I was reading about removing a resister to force it to run at 167mhz so the clock speed won't change. I just wanted to confirm because I might pick up a dual 867 for really cheap (<$100) and use the PSU to test my 1ghz and dual 1.25 mdd's, or just swap in the faster processors. I only have PC2100 ram too so that probably won't work out since I'll need PC2700 if I overclock it :(.
     
  4. TimmyDee macrumors member

    Joined:
    Feb 20, 2007
    #4
    That's true about the RAM. I used to have a dual 867 MHz myself, and I kicked around the idea of upgrading the bus speed. Problem was, I had 1.25 GB (!) of 133 MHz RAM. It was far too costly to upgrade at the time, and by the time it became cost effective, it just wasn't worth it. Oh, well.

    Have fun with the machine, though. Although they were often panned as "wind tunnel" Power Macs, I think they were good, powerful machines for the time. And they still probably run things pretty well.
     

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