will cross fired 5870s be able to boot in osx?

Discussion in 'Mac Pro' started by revilate, May 28, 2012.

  1. revilate macrumors member

    Nov 4, 2011
    i've been playing bf3 on bootcamp on my mac pro with a single 5870, and while i can play at an average ~60 fps on pretty decent graphics settings, i'm interested in getting the most i can out of this machine.

    i know the only gpu options for a 5,1 mac pro are either two 5770s or one 5870s... but i had an idea...

    i know these mac pros only have around a 1000w psu, but the 5870s not only run cool, but they also run very efficient compared to other cards, taking only about 27w at idle and 188w at full load.

    while the board on the mac pros only has two six prong power plugs for attaching a gpu, i figure i could use two six prong to two eight prong splitter cables to connect two 5870s in the mac pro.

    i only have a few questions for anyone that may wanna chime in:

    will that power going through only those two outputs fry the board or connections?

    while two 5870s would undoubtably work boot camped in windows, just like they would in any normal windows machine, what would happen if i left them crossfired and booted up into osx? would osx work normally as it does with a single card and just ignore the other card or would i get a black screen or whatever?

    if there's not enough power with the stock psu, would it be possible to switch out for say a 1200w psu to replace it?

    i know it'd make the inside of the mac pro a bit ugly and un-apple like, but would it be possible to bypass the six prong power connectors on the board and just run a power cable directly from the psu to the cards to avoid any board frying?

    what do you guys think?

  2. revilate, May 28, 2012
    Last edited: May 28, 2012

    revilate thread starter macrumors member

    Nov 4, 2011
    sorry about that, missed your post in that big thread.

    i might try to call apple to see what the rating or limit is of those power connections... if the rating is within the consumption of a single 5870 per connection, i'll go for it and report back here.

    on further research, it seems that a single 5770 has a maximum power consumption of 112w... if two of those are supported by apple themselves, this at least indicates that 1) we at least have 112w of power able to be held by a single connection and possibly more or 2) this could possibly be the maximum amount of power allocated to a single connection on the board form the psu...

    there's also a video tutorial on youtube from a guy who seems to easily get a 5870 and a 5770 running in his mac pro. what this indicates to me is that (assuming he's not using an auxiliary power source) the connections can at least handle 300w (5770 + 5870 max load power consumption). if the connections could handle at least 76 more watts (the difference between two 5870s), this could easily and safely work.

    i've heard of a lot of people (with windows machines) just getting another 5870 and cross firing them because supposedly they give next to near the same performance as a single 7970.
  3. Cindori macrumors 68040


    Jan 17, 2008
    If you call Apple you will probably have to speak to 5 people who don't know what a Mac Pro is, then speak to 10 people who don't know what a power rail is, then finally speak to a real engineer that will tell you exactly what the website says, aka that you should use the Mac Pro as intended and that they don't give support to anything else.

    I'm not saying it won't work using two 5870's from the two onboard PCIe power connectors, I'm saying that I wouldn't do it tho. Might not fail until months later.
  4. Spacedust macrumors 6502a

    May 24, 2009
    I can only confirm this:

    1. Two HD5770's crossfired boot into OS X.
    2. Two HD5770's where one is Apple, the other is flashed boot into OS X.
    3. When Apple card is paired with flashed card the flashed card will be unlocked to 5 GT/s bandwidth !
  5. revilate thread starter macrumors member

    Nov 4, 2011
    yea no kidding lol...

    "hi, i'm calling with a question about my mac pro."
    "oh sure, how can we help you with your macbook pro?"

    that's a good point and worries me a little bit... is after months of gaming and possible stress (if it would stress) on the pose rails them failing...

    dziekuje moim przyjacielem :)
  6. derbothaus macrumors 601


    Jul 17, 2010
    Great Applecare summery. I never learn and have been through this at least 20 times. Same result each time. You can easily insert differing models into that equation.
    OP- you should not deal with dual 5770's. Not worth it. Some games in Win will use adequately but you don't ever double your performance and a 5870 is pretty close to 2x as fast as a single 5770 anyway. Not sure if you were toying with this idea or just interested in 2x5870's. Unfortunately AMD just sucks for BF3. Nvidia made sure of it. A GTX570 beats an AMD 7970 which is just ridiculous.
  7. MacVidCards Suspended

    Nov 17, 2008
    Hollywood, CA
    If you do try running 2 5870s from single power connection, please have a video camera running and a fire extinguisher handy. WIll make a GREAT Youtube video. You'll be kicking some Ceph butt in Crysis 2 when you blow up something and the Mac Pro bursts into flames. If you have a dog sleeping by the Mac Pro when the flames start it will be especially funny as he wakes up and starts barking. Then Grandma can run in screaming, and blast the Mac Pro with the Fire Extinguisher. It will be viral in days !!!

    Among other things your math is off. Whenever you are adding up power for PCIE cards you need to include 75W as being from the slot connection itself.

    This just made me realize that the REAL answer would be for someone to come up with PCIE connectors that just ended in 6 pin plugs. So if you weren't using slots 3 & 4 you could turn each of them into 6 pins and have enough internal power.

    There is a thread here from a thorough guy who didn't want to become a youtube star. He used a dedicated GPU PSU in the drive bays. Nice long thread complete with pretty color pictures here on this board. I'd start in the upper right corner, the "Search Forums..." box.
  8. Photovore macrumors regular

    Dec 28, 2011
    There was a thread on some board somewhere (with photos) wherein somebody put two 5870s into a Mac Pro; they bought an external power supply and ran wires in through an empty pci hole having removed its plate. That's what I'll do if necessary.

    You might want to connect the two grounds, too, though the wall circuitry is probably enough.
  9. theSeb, May 29, 2012
    Last edited: May 29, 2012

    theSeb macrumors 604


    Aug 10, 2010
    Poole, England
    I recall reading that thread on this forum.

    Edit: Found it.

  10. bax2003 macrumors 6502a


    Dec 25, 2011
  11. lixuelai macrumors 6502a

    Oct 29, 2008
    It depends on how the PSU in the Mac Pro is built/designed. Typically 900w is more than enough for 2x 5870 assuming the PSU is of decent quality and rating is not heavily inflated. I am sure the Mac Pro has a decent PSU. What is an issue however is if or how the rails are split. If 12v is split into multiple rails and all the PCI-E connectors are on the same rail you will overload that rail (each rail is usually 18 amps+ and the highest split 12v rail amperage Iv seen is like 24 amps).
  12. Photovore macrumors regular

    Dec 28, 2011
    Good find, though I'm not sure it was the thread I was talking about; think that one had a photo of the wires running in the back of the Pro.

    Certainly shows that it's easily doable.
  13. Spacedust macrumors 6502a

    May 24, 2009
    Crossfire doesn't work fine on Windows on latest drivers !!! The last one that will work is Catalyst 10.11. All newer will cause BSOD when checking Enable Crossfire. This happen when at least one Apple card is installed.

    I have to remove my second HD5770 card, because it was working slower on Crossfire than on a single card in most of the games.
  14. Wardenski macrumors 6502

    Jan 22, 2012
    I think the PSU would handle it but the logic board may not as some have already said. By splitting two 6 pins into two 8 pins you will draw more current than designed.

    If you get a dedicated power booster you could in theory get a 5990 and have a Tri-fire set up. OSX should ignore the 5990 but use the Apple 5870.
  15. ghislain macrumors member

    Apr 22, 2009
    yes 2 crossfire 5870 boot in OSX on my 2010 mac pro. Concerning power supply, I use an external PSU because if on board power supplies slots are sufficient when the 2 GPUs are used in low power supply mode, this is no longer the case when they are used, for instance, for 3D gaming. In this case, GPUs stay in low energy mode, so there is no benefit to have 2 crossfire cards (tested with GPU-Z).

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