Why not desktop GPU?

Discussion in 'iMac' started by ventuss, Oct 6, 2013.

  1. ventuss macrumors 6502

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    Oct 9, 2011
    #1
    If the iMac uses desktop CPU, why keep mobile GPU?
     
  2. craigmartin macrumors newbie

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    Sep 12, 2013
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    UK
    #2
    Dunno but I'd guess is something to do with how much heat is created by desktop GPUs... but I'm probably wrong ;)
     
  3. Serban Suspended

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    Jan 8, 2013
  4. jcbhammond macrumors member

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    May 3, 2010
    #4
    My guess would be heat and power requirements. iMacs are fairly thin too so Apple would have to design their own GPU or provide a PCI expansion slot which increases width. Add to that that it has to power an internal display as well and that the majority of the iMac market just doesn't need the power, I'd say the cost benefit for designing and implementing it isn't worth it. In my experience for most everything, but gaming of course, mobile GPU's work pretty well.
     
  5. asmallfly macrumors newbie

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    Jan 24, 2013
    #5
    Desktop GPUs have many more transistors than CPUs, (my 7950 in my gaming PC has 4.3 billion, 4 times as many as a typical i5 CPU) and consequentially, require more power to push the electrons through them. This creates resistance, and resistance creates heat. This heat has to be removed, and high performance GPUs in desktop computers usually have huge heat sinks and fans. There is no space inside an iMac for these thermal solutions, and consequentially, they must use lower power mobile versions.
     
  6. Gherkin macrumors 6502

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    Apr 9, 2004
    #6
    Apple likes to keep clear distinctions with their computer lines.

    If you want a desktop class graphics card, there's the Mac Pro line.

    You have to be doing some very demanding stuff for the maxed out late-2013 iMac to not be enough power.
     
  7. ventuss thread starter macrumors 6502

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    Oct 9, 2011
    #7
    A mobile GPU sits on the logic board, or is it an attached board?
     
  8. asmallfly macrumors newbie

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    Jan 24, 2013
    #8
    Mobile GPUs, like mobile CPUs are permanently soldered to the main board.
     
  9. Bear macrumors G3

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    Sol III - Terra
    #9
    See this thread for more discussion on the subject.

    Not necessarily true. Some iMacs have had the GPU on a separate card.
     
  10. Steve121178 macrumors 68040

    Steve121178

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    Apr 13, 2010
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    Bedfordshire, UK
    #10
    Desktop GPU's are huge and require a lot of power and produce a lot of heat. That's why you'll never see another desktop-class GPU in an iMac.

    It's not a big deal as high-end notebook GPU's are ideal for AIO machines.
     
  11. MikeChicago macrumors member

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    Sep 30, 2013
    #11
    This isn't always the case. The base 21.5" iMac has a CPU that is permanently soldered to the motherboard, but the 27" iMac does not. I'm pretty sure, however, that the GPU is soldered on permanently in both models. I could be wrong.
     
  12. TwoBytes macrumors 68020

    TwoBytes

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    #12
  13. RedReplicant macrumors 6502a

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    Mar 31, 2010
    #13
    GPU is built into the motherboard on Late 2012+ iMacs, earlier models have MXM cards that are swappable.
     
  14. elithrar macrumors 6502

    elithrar

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    May 31, 2007
    #14
    ... and as touched on in that thread:

    GTX 780M TDP = 100W.
    GTX 770 (desktop) TDP = 230W.

    The 780M is a slightly down-clocked (but otherwise identical) 770 desktop card. That's pretty darned good given the substantial TDP difference.

    For reference, an additional 130W is almost like adding two more i7 Haswell CPUs (70W TDP each), stacked on top of each other. That's very hard to cool, even if Apple reverted to the thicker 2011 chassis. High-end desktop cards are >= 10.5cm long, have a huge heat-sink, two fans and take up 2 PCI-E slots (and then some).
     
  15. RedReplicant macrumors 6502a

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    Mar 31, 2010

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