Why not desktop GPU?

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

  1. ventuss macrumors 6502

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

    Sep 12, 2013
    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

    Jan 8, 2013
  4. jcbhammond macrumors member

    May 3, 2010
    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

    Jan 24, 2013
    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

    Apr 9, 2004
    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

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

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

    Jul 23, 2002
    Sol III - Terra
    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 601


    Apr 13, 2010
    Bedfordshire, UK
    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

    Sep 30, 2013
    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 68030


    Jun 2, 2008
  13. RedReplicant macrumors 6502a

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


    May 31, 2007
    ... 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

    Mar 31, 2010

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