OS X 10.5.3 (and beyond) Increases CPU Power Draw?

Discussion in 'Mac Pro' started by jsurpless, Sep 3, 2009.

  1. jsurpless macrumors member

    Aug 6, 2009
    Hi all

    I've got another ongoing thread (2006 Mac Pro Elevated CPU Temps) where I've been attempting to determine why my 2006 Mac Pro was running so much warmer than I recall at time of purchase...

    By sheer luck, I seem to have stumbled on the cause... when I first noticed it, I was running 10.5.7 with the CPUs idling around 130F or so... as noted in that thread, I tried all sorts of things such as cleaning the dust out, reapplying the thermal paste, etc... all of which had no impact... for an unrelated issue, I decided to re-install OS X 10.5 base version and I was shocked to discover my CPU temps back down in the mid-90s F or so...

    I happened to have taken some screenshots of Hardware Monitor and was able to compare them against the current readings... under OS X 10.5 -> 10.5.2, each CPU draws ~10W @ idle; under 10.5.3 and beyond, the CPU draw increases to ~30W @ idle. Naturally, this extreme increase results in the aforementioned temperature increase... I'm not sure as to the cause but my immediate suspicion is that some low-power CPU mode is disabled in the later revisions...

    I've spoken to Apple about this and they're looking into it but in the mean time, I was wondering if anyone has any input on this?

  2. Infrared macrumors 68000


    Mar 28, 2007
    Is that something to do with SpeedStep?
  3. jsurpless thread starter macrumors member

    Aug 6, 2009
    I'm not sure what is meant by "SpeedStep"?
  4. gugucom macrumors 68020


    May 21, 2009
    Munich, Germany
    Speedstep is a technology where the CPU steps down the internal voltage and frequency when it senses idle.


  5. jsurpless thread starter macrumors member

    Aug 6, 2009
    So maybe this has been broken in some capacity in 10.5.3 and after?

    My CPU voltages are ~1.3 and ~1.15 in 10.5.3 and 10.5.0, respectively...
  6. jsurpless thread starter macrumors member

    Aug 6, 2009
    Are others observing similar behavior? What are people seeing for power draw at idle?

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