How are the nMP GPUs multiplexed?

Discussion in 'Mac Pro' started by Cubemmal, Dec 22, 2013.

  1. Cubemmal macrumors 6502a

    Joined:
    Jun 13, 2013
    #1
    This was somewhat discussed a while ago, but how do they allocate 2 GPUSs for three ports? According to Apple the bottom two are Controller 0, the two left above those are Controller 1, and the two right are 2.

    Say I connect 3 4k monitors, does one GPU get two monitors? Does this imply internal Crossfire usage?
     
  2. Gav Mack macrumors 68020

    Gav Mack

    Joined:
    Jun 15, 2008
    Location:
    Sagittarius A*
    #2
    PCIe 3.0 supports cards connected via the bus eliminating the need for crossfire. On efficiency alone I'm taking an educated guess they have gone down that road..
     
  3. VoR macrumors 6502a

    Joined:
    Sep 8, 2008
    Location:
    UK
    #3
    Not that I've looked closely, but It's a proprietary card and they could build it into the connector, but crossfire isn't required for multi-monitor or ggpu computing.
    The 7970 and 280x (rebranded 7970 with GCN) both require a physical bridge, the D700 is just an under-clocked/voltage version of these tahiti based boards.
    The hawaii based 290 cards do their crossfire through pci-e (and pci-e 3.0 isn't a requirement for this, 2.0 works just fine).
     
  4. Cubemmal thread starter macrumors 6502a

    Joined:
    Jun 13, 2013
    #4
    Sure they could run two monitors off one card but that's an asymmetry and difference in performance potentially. I would think Apple would advise us as to which ports got the dedicated GPU.
     
  5. goMac macrumors 603

    Joined:
    Apr 15, 2004
    #5
    There is no Crossfire support under OS X at present. Each display is driven by a single card.

    You can use one card for OpenGL and another for OpenCL within the same app, however.

    Source: A little biddy.

    I don't know what port goes with what card.
     

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