AMD Radeon R9 M290x 2GB vs M295X 4GB - power consumption

Discussion in 'iMac' started by iConnected, Oct 31, 2014.

  1. iConnected, Oct 31, 2014
    Last edited: Oct 31, 2014

    iConnected macrumors 6502a

    iConnected

    Joined:
    Feb 17, 2011
    #1
    I'd appreciate some advice regarding power consumption, please (I can't find answers in other threads about choosing between these cards).

    Assume that I choose the M295X for reasons including:

    - catering for occasions when my present use might benefit from the added power (perhaps likely to be rare).
    - future-proofing to accommodate changes in requirements from software (OS X and applications).
    - protecting re-sale appeal and value.

    The power consumption chart http://support.apple.com/kb/ht3559 shows two Retina iMac specs, one with the M290X and the other with the M295X, along with other differences.

    Both specs have the same power consumption at idle. However, the base spec shows 176W CPU Max power consumption vs the higher spec at 288W CPU Max.

    Questions:

    1. Does CPU Max also include an assumption of maximum graphics load? (ie both the graphics card and CPU working hard)

    2. How much of that difference in CPU Max power consumption between the two specs is attributable to the M295X card?

    3. Perhaps most importantly, if / when I am only doing undemanding stuff on the iMac, would both cards use the same power? (if so, an indication of what is considered undemanding would be helpful).

    I'm sure you've guessed where I'm coming from. I don't want to run a power hogging iMac (relatively speaking) day in, day out for the next few years just for the sake of occasional benefit and possible future need or resale value.

    But if the typical running costs would be the same or thereabouts, I'm happy to choose the upgrade.

    Thanks!
     
  2. FredT2, Oct 31, 2014
    Last edited: Oct 31, 2014

    FredT2 macrumors 6502

    Joined:
    Mar 18, 2009
    #2
    I don't think there's any way of answering your questions without setting up a trial where one would measure power usage under different scenarios of CPU vs GPU load, but I don't think it really matters. For normal tasks it's not going to be using that much energy. Both models have the same idle rating.

    Update: I did some of the testing for you. Here are some measurements I got:

    Idle: 35 watts
    CPU load: 130 watts
    GPU load: 175 watts
    CPU+GPU: 230 watts

    Just using the computer, running Safari,Mail, playing videos, etc, it stayed mostly in the 50 to 75 watt range. Browsing through full-size images in Lightroom took it to 120 watts.
     
  3. iConnected thread starter macrumors 6502a

    iConnected

    Joined:
    Feb 17, 2011
    #3

    Thank you very much for taking the time and trouble to run those tests - those figures certainly sound reassuring.
     

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