HD 5850 in crossfire on P7P55D sigh! without realizing that I have a motherboard that only supports second GPU at x4, I still got myself an Asus HD 5850 DirectCU TOP. My first card is HIS HD 5850 iCooler V. Both individually are working fine. I listened to opinions here and decided to go with identical families of GPU to crossfire.

I put them in crossfire mode with Asus as primary, and HIS as secondary. And no matter what I try, GPU-Z shows GPU 2 as Crossfire : Disabled. Using MSI Afterburner, I matched HIS's clocks with Asus's (I did not touch any voltages). I am running official Catalyst 11.3 and I have enabled that checkbox for crossfire in Catalyst control center. But GPU identifier shows just a big number 1. The diagnostic window in Catalyst for crossfire setup is blank.

Just for the record, my monitor is connected to the primary card's DVI-D output (ASUS) since I don't have capability to use that HDMI output.

Why is this not working or seems to be not working?

Secondly - I read many opinions bashing X16/x4 crossfire setup, and many said it is definitely some improvement if not as good as x8/x8 or x16/x8 or x16/x16. What's your opinion? My system is LGA1156 based. If it is really that hurtful, should I save up for a better motherboard (which one?)

Thank You.
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  1. Alright, so did you connect the crossfire bridge cable between the cards?

    Have you gone through your BIOS for options regarding PCIe? Possibly something got turned off.

    Did you do a complete driver delete and reinstall after installing the 2nd card?

    As for the bandwidth thing, it shouldn't make too much of a difference.
  2. Crossfire bridge is connected.

    There are no PCIe related options in BIOS as far as I saw. I just read somewhere that GPU-Z is not a very good tool when it comes to displaying such statuses. And Catalyst Control Center's diagnostic should indeed remain empty when in crossfire.

    Yes I swept all the drivers clean and used 11.3 latest. used MSI Afterburner to match clocks to the slower card.

    I started a game and saw that both card's temperatures went up, and both showed some GPU usage (MSI Afterburner), so they might just be working alright!

    Why are people saying x16/x4 is bad if bandwidth does not make a difference? I have heard numbers as high as 30% performance hit on the second card at x4. GPUz does display it at x4 but says it is disabled. Is it worth upgrading to a "better" motherboard in this regard? Much appreciated response.
  3. Sounds like it is working then.

    As for the 16/4 thing, it's really hard to say. You can read this for some idea, but unfortunately they don't test your situation:,2696.html

    Are you on Win7? Try running 3DMark11 and/or Vantage and maybe we can compare GPU scores, they should be close if I clock my cards at the same as yours. (Let me know what the clocks are).

    As for upgrading, I have an Asus P7P55D Pro and it supports 8x/8x and it even has a 3rd PCIe 16 slot running 4x through the southbridge.

    However for future GPU upgradeability (because, really, your i7 860 should be a good enough CPU for many years) you might want to look at an NF200 motherboard. These have 16x/16x and 8x/8x/8x/8x support thanks to the NF200 chip. They're hard to find though and very expensive, the P67 versions are around $300.

    Wait, found some :D
  4. That's exactly why they seem to be that expensive, well at least one of the reasons.

    I think there are many quite cheap ones with X16/X8. I might just go with one of those as X8 is good enough.
  5. Best answer
    i thought you got it working? i wouldnt get another motherboard if its working. there are plenty of articles with p55 xfire reviews. they all point to little to no difference in performance exceps for certain games mainly at really high resolutions. google is your friend
  6. ^One of the first articles from that google search:

    The list of motherboards to avoid if you want to use Crossfire or SLI
    Here’s a list of motherboards whose second PCI-Express slot is connected at 4X with the P55 and that I urge you to avoid if you plan to build a Crossfire or SLI system:

    ... ASUS P7P55D

    So yeah it's not an optimal set up, but again, it shouldn't be hurting too much...
  7. Yes I was just reading through that. And while I can always spend another 100 dollars and get ASRock motherboard, not sure if the price justifies the LGA1156 setup, after all. My second GPU cost me 100 dollars and it is the very excellent ASUS DirectCU OC card.

    This compares 5870 scaling and the performance drop for this card from x16 to x4 (CF) is no more than 8-10%

    I guess I shall just live with what I have right now. If I go to another family of socket, these two cards will still last for a long time, at least until I am bored of gaming :)

  8. Best answer selected by pinaklonkar.
  9. In closing, anyone stuck with X16/X8 or X16/X4 rails for crossfire or SLi, the performance drop may not justify buying of a new motherboard.

    It could be really noticeable in some games, where performance hit because of high end GPU running on X4 PCIe rail, but you really can't win them all.

    If you are planning for a NEW build, though, it's better you get a X8/X8 at least, because not many cards really need/utilize X16 to the fullest potential anyway.

    EDIT: I installed the two cards in crossfire and they are working fine. But there is microstuttering in some games and it is best to disable CF when playing these games specifically, mostly two years and older games titles are subject to this. In some games, tweaking the graphics settings or modifying fan profiles through MSI afterburner is one of the way to reduce or get rid of the microstuttering. But it is a problem, and many people actually seek single GPU solution.

    I am going to live with two cards :) feels cooler :P
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