Graphics Card+Molex/PCI-E = ?

Discussion in 'Mac Pro' started by DualBooterOSX7, Jul 25, 2010.

  1. DualBooterOSX7 macrumors newbie

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    May 6, 2009
    #1
    So I have a 2008 8-core Mac Pro (Model 3,1) and I'm dual-booting OSX and Windows 7. I want to use Windows for gaming.

    It's lovely and all but I want to get a new graphics card for the Windows side, and I've settled on the GTX 460.

    I understand that the GTX 460 will not work on the OSX side, and I want to have both the current 8800 GT and the new GTX 460 installed while using the 8800 for Mac and the GTX 460 for Windows. I do not want to have to physically remove the GTX 460 every time I want to boot into OS X, I want the OS I am using to automatically use the appropriate card without physically removing or installing anything.

    I read this thread and it looks like what I'm trying to achieve is possible, but I'm confused as to the details of it.

    1. Should I purchase this Molex 4-pin splitter or this PCI-E splitter? Is there a difference in installation methods?

    2. Are there any additional peripherals I need to purchase to achieve my goal?

    Thanks so much! I've been searching for hours and I can't wrap my head around this stuff--I've never had to open up my computer so I'm a little nervous.
     
  2. CaptainChunk macrumors 68020

    CaptainChunk

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    #2
    Using the PCI-E splitter would mean less cable clutter, as a Molex splitter would leg off of the power connections for the optical drive bays. I would use the PCI-E splitter, personally.

    In Mac OS X, the GTX 460 would essentially be ignored as an unsupported device in one of the PCI-E slots. In Windows, you can simply disable the driver for the 8800 GT and everything should work fine.
     
  3. DualBooterOSX7 thread starter macrumors newbie

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    May 6, 2009
    #3
    CaptainChunk strikes again, thanks a lot! So I need 2 of the splitters right? Are there any tutorials or instructions out there for using them?
     
  4. Cindori macrumors 68040

    Cindori

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    #4
    not guaranteed that mobo pci ports can deliver enough power for splits
     
  5. DualBooterOSX7 thread starter macrumors newbie

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    #5
    What is a mobo (motherboard?) and what do I do if my graphics card is underpowered? Will I have to go Molex?
     
  6. Cindori macrumors 68040

    Cindori

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    #6
    attempting to draw too much power can kill your mobo. I'd go molex. instructions in sig.
     
  7. DualBooterOSX7 thread starter macrumors newbie

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    May 6, 2009
    #7
    OK, one more question, on of the posters in the topic said "-no one wants to switch graphics cards every time they change the OS"

    What did he mean there? I won't have to keep taking out the graphics card right? Is the switch he's referring to a software one?
     
  8. MacVidCards Suspended

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    Hollywood, CA
    #8
    Since you are already planning on having 8800GT in there for OSX, it can be used in conjunction with ATY_Init to run the 460 in OSX. (you would also need to install drivers that Nvidia so nicely "leaked" to us)

    Hasn't been done yet but since 480 works, good chance 460 will.

    The 480 is running at about aquarter of it's potential...ie, similar to an 8800GT.

    You might as well do this, would reduce the monitor cable fiddling.

    8800 could be dedicated Physix card in Windows.

    You should most definetely plan on using power from both supplied plugs AND the Molex. DVD drives use FAR less power than video cards, so I doubt that Molex has enough juice all by itself, no reason for Apple to run lots of power to something that only needs tiny amount.

    I just grabbed a DVR104 from Apple. It is rated to draw .7A on 12V and 1.4A on 5V. These numbers are MINISCULE compared to GPU current draw. Don't count on big fat power leads to a part of machine that uses .7A.
     
  9. slughead macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #9
    I tried that with an X1900 and my 2006 mac pro and it didn't work.

    It drew too much power down the molex and it wouldn't start up. Granted, I had my ancient 80GB 10krpm Raptor hooked up to the same molex drawing a lot of power.
     
  10. CaptainChunk macrumors 68020

    CaptainChunk

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    #10
    Good point Cindori, although I think it would be helpful if there were specs published on how much current the "booster" PCI-E ports on the logic board actually supply. Sort of a mystery...

    But take for example, EVGA's GTX 285 for the Mac. It's need two auxiliary PCI-E power leads and according to EVGA, it needs a minimum of 40A (+12V) to operate. So assuming the PCI-E slot is supplying its maximum of 75W (6.25A on a +12V rail), it needs an additional 33.75A, or roughly 16.9A from each auxiliary power connection.

    A GTX 460 in contrast, needs about 24A minimum to operate. Using the same math, that would be 6.25A from the PCI-E slot plus about 8.9A from each auxiliary power connection to run the card. Assuming a GTX 285 draws the upper limit of what the Mac Pro's PCI-E boosters are able to supply, that would leave us with about 8.0A remaining for each booster when running a GTX 460 by itself.

    An 8800 GT card (according to NVIDIA), needs 22A. So, yeah...I suppose that would be cutting things close with an 8800 GT also running in the same machine, as it would only be getting about 15A total amps sharing one of the boosters (or the GTX 460 getting 7.0A less than it actually needs).

    But again, that's assuming a GTX 285 is really saturating all the available power from the logic board headers. Perhaps this isn't really the case, but I suppose it would be a gamble to find out...

    But the flip-side of the argument would be how much current the Molex connectors are able supply, considering they're intended for connecting optical drives (which use almost NO current). Hard to say...
     
  11. DualBooterOSX7 thread starter macrumors newbie

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    May 6, 2009
    #11
    You've totally lost me, I'm very new to this. Are you saying I can use 460 on both OS X and Windows 7 using this "ATY_Init"? Could you direct me to a tutorial on how to do this? If it's complicated, I'd be satisfied with just having 460 run on Windows.

    Is all your saying is that I should plan to use both the Molex cables and the ones that come with the graphics card? In that case, that doesn't change anything right?

    With the Molex splitter and everything that comes in the 460's box, can I achieve all my goals?

    Can anyone confirm that they've achieved satisfactory results using a similar setup?

    Thanks everyone for all the help, please bear with me, I'm not a total neophyte but some of this stuff is a little over my head.
     
  12. MacVidCards Suspended

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    Nov 17, 2008
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    Hollywood, CA
    #12
    read the thread on GTX480 working in Mac Pro

    It's so simple, a caveman can do it.

    You will need to use BOTH of the onboard GPU power connections AND use the Molex.
     
  13. nanofrog macrumors G4

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    May 6, 2008
    #13
    Yes, mobo = motherboard.

    That said, the traces on the board likely won't be able to handle the current draw for both cards, nor is the Molex connector suitable (same reason, not enough current available).

    The best solution IMO is a 5.25" bay PSU meant for graphics cards. Cheap too.

    You can also use a standard PC PSU by just jumping the green and black wires (turns it on). Ugly as it's external, but it works.
     
  14. slughead macrumors 68040

    slughead

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    Apr 28, 2004
    #14
    That thing is neat, but I don't think it'll work in a mac pro. How are you going to get the AC cord outside the case?
     
  15. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #15
    Take the cover off of a PCIe slot, say slot 3 or 4 (PCI slot cover - that didn't change, just the slot itself), just as you'd do in a PC, unless you cut/drill a hole to fit it through (I presume case mod is out of the question). :D
     

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