SLI under windows on new MacPro

Discussion in 'Mac Pro' started by Abidubi, Mar 4, 2009.

  1. Abidubi macrumors 6502

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    #1
    So it was my understanding that all the mac pro motherboards have supported SLI, only that it does not work under OSX. Do you need to have special SLI enabled nvidia cards or would the stock 120GTs work? ie, if you were to purchase it with 4 120GTs would they all work using SLI under windows?

    Just throwing it out there as I a) don't have the cash to buy 4 and b) I much rather have a fast 4870 that works in both mac and windows.
     
  2. Tallest Skil macrumors P6

    Tallest Skil

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    #2
    There aren't SLI connectors on the GT 120s, so you'd have to have Windows-only cards to do it this time around.

    And, while Tylersburg in general has SLI support, we don't know if Apple's version does.
     
  3. Chaos123x macrumors 68000

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    #3
    Has Nvidia ever made their own Mac Cards like ATI has?
     
  4. Tallest Skil macrumors P6

    Tallest Skil

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    #4
    They don't even write their own drivers. Why do you expect them to make their own cards?
     
  5. Abidubi thread starter macrumors 6502

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    #5
    I see. For some strange reason I thought that SLI didn't need any special connectors and that it worked completely through the motherboard. Oh well. At least crossfire works.
     
  6. Chaos123x macrumors 68000

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    #6
    Your right, but the mother board needs the Nvidia chipset to work.

    i am sure this is a Intel chipset and they did not get the license for Nvidia for this Logic Board.
     
  7. Tallest Skil macrumors P6

    Tallest Skil

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    #7
    Oh, no. Tylersburg is the only Intel board to have SLI support straight from nVidia.

    So whether it's true Intel Tylersburg or nVidia's equivalent, it should have it.
     
  8. Salavat23 macrumors 6502

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    #8
    The current Mac Pro motherboard does not support SLI.

    Crossfire, however, is supported under Windows.
     
  9. Tallest Skil macrumors P6

    Tallest Skil

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    #9
    Do you know that?

    Tylersburg itself supports SLI. With the Gainestown Mac Pro, at least, Apple has to be using a variant of Tylersburg.
     
  10. m1stake macrumors 68000

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    #10
    The X58's are a pretty mixed bag; some of them have the chip on them, and some of them don't. All of them support SLI. Point being that one way or another, SLI works.
     
  11. Salavat23 macrumors 6502

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    #11
    Nvidia has to first put a seal of approval on the motherboard to have it officially support SLI. Yeah, Tylersburg supports it, but its useless without Nvidias "approval".

    Look what happened to some of the X58 boards. Some of them got SLI months later when Nvidia said it was ok and released a software update unlocking SLI.

    As it stands now, I REALLY doubt the Mac Pro supports SLI.

    And to the above poster, its not a chip thing. Its the difference between a BIOS/Revision that supports it, and one that does not.
     
  12. Tallest Skil macrumors P6

    Tallest Skil

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    #12
    But they have. That's what I'm saying. :confused:

    In OS X, I agree 100%.

    In Windows, we'll see.
     
  13. m1stake macrumors 68000

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    #13
    Half of the boards use the NF200 chip that allows SLI to run, and half of them have it built into the BIOS.
     
  14. Salavat23 macrumors 6502

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    #14
    Where does it say that? Gotta read the long PDF files lol.
     
  15. Tallest Skil macrumors P6

    Tallest Skil

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    #15
  16. VirtualRain macrumors 603

    VirtualRain

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    #16
    There's a lot of misinformation here about how SLI works and under what conditions.

    Prior to Nehalem and X58, SLI would only work on nvidia chipset based motherboards. However, this had nothing to do with the motherboard or chipset, it was actually a check performed by the drivers... if a suitable nvidia chipset was present, SLI would be enabled, otherwise it wouldn't. Someone actually hacked nvidia drivers to work on non nvidia motherboards a couple of years ago but nvidia quickly rectified that and encrypted the keys to ensure that didn't happen again.

    On Nehalem and X58, nvidia (so far) cannot develop a chipset replacement for X58 (tylersburg) so rather than be locked out of the multi-gpu market on this new platform, decided to offer motherboard manufacturers two options to get SLI support working on their boards:
    1. Initially Nvidia said board vendors could implement the NF200 PCIe bridge chip which would not only enable SLI, but also offer a 2-1 PCIe bridge to provide additional PCIe lanes on the motherboard. The problem with this solution was that the chip runs hot and takes precious board real-estate so many motherboard manufacturers complained, leading to...
    2. Under pressure from top-tier board manufacturers like ASUS, Gigabyte, and others, Nvidia offered to license SLI on a fee per board basis and by doing so, would enable the manufacturers to enable SLI flags in BIOS. Thus offering a completely hardware free solution for SLI.

    Nvidia charges around $30-$50 for either approach on a per mainboard basis.

    Note that it's up to the drivers to detect either the presence of the NF200 or the licensed BIOS flags implemented by the motherboard manufacturer.

    Hence, it's not true that X58/Tylersburg supports SLI... the chipset really has nothing to do with whether SLI is supported or not. It's all about whether the vendor implemented either of the two solutions outlined above.

    Finally, SLI benefits from, but does not require the SLI bridge connectors. The SLI bridge connectors that connect the cards at the top enable direct chip to chip communication without using the PCIe bus which can provide a performance improvement, especially at high resolutions. However SLI will run without bridge connector and use the PCIe bus instead if it has to although stuttering is a common problem when not using the bridge.

    As for Crossfire, ATI doesn't require motherboard manufacturers to license anything. ATI drivers simply look for the presence of multiple compatible cards in the system, and if present, enable Crossfire. Hence, Crossfire works on any system.

    With respect to multi-gpu support on the Mac Pro, unless Apple implements either of the two solutions above, SLI will not work on the Mac Pro. Apple has no need or interest in doing this for obvious reasons (i.e. supporting multi-gpu scaling under windows just isn't a priority for Apple). Since Crossfire works on any Windows system, it will obviously work on the Mac Pro under Windows.

    Hopefully that clarifies things a bit.
     
  17. Quu macrumors 68020

    Quu

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    #17
    VirtualRain is correct about almost everything he said.

    NVIDIA licenses SLI to motherboard makers, they can either use their PCIe Bridge Chip or BIOS mod to bring SLI to there non-NVIDIA motherboards.

    It is the NVIDIA drivers that check for SLI flags on the Motherboard, if these are not present it will not enable SLI.

    The NVIDIA drivers in the past have been modified to detect the required strings on any Motherboard with dual NVIDIA PCIe cards installed (ULI are famous for doing this before they were acquired by NVIDIA)

    The Mac Pro does not and will not include the NVIDIA BIOS Flags as Apple have no need to license SLI for OS X usage. The Mac Pro also does not have a BIOS per-say it emulates one via EFI but I'm not sure how they would exactly work it all out.

    The NVIDIA cards do not require the SLI Bridge as Virtualrain said it is recommended to use one or you may have degraded performance and stuttering on some of the more heavy-duty cards but the low-end and mid-end can usually work without the bridge with a small loss in performance.

    Finally Crossfire does not work on any board. ATi Drivers like NVIDIA ones look for Chipset, BIOS and other flags before it enables Crossfire. Which is why you cannot get Crossfire working on 680i 780i and 790i motherboards (NVIDIA Socket 775 boards) however ATi's licensing is better so if the motherboard wants to include it (which most do) they add in the flags to their BIOS which the drivers will happily detect and enable Crossfire multi-GPU support. Some forums like Extreme Systems have posted hacked ATi drivers in the past to get Crossfire working on NVIDIA and other motherboards.

    It is important to note that Crossfire also does not require a bridge but most cards will ship with one anyway, a flexible one that can adjust across different sized gaps. The only thing Virtualbox was incorrect on was the Crossfire support automatically working on any Motherboard. Other then that his all good, I repeated much of the information he had just as confirmation I know people on this board have a hard time believing things sometimes :p
     
  18. VirtualRain macrumors 603

    VirtualRain

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    #18
    Thanks for the clarification, Crossfire is not my area of expertise... ;)
     

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