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Crossfire - What are the rules?

Discussion in 'AMD / ATI' started by 1933 Poker, Nov 11, 2009.

  1. 1933 Poker

    1933 Poker New Member

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    Hello. Just wondering if you can not only mix gpu manufacturers when crossfiring, but if you can also mix gpu models, eg 4870+4850??
     
  2. Easo

    Easo

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    yes
    but they will run on 4850 speed.
     
  3. 1933 Poker

    1933 Poker New Member

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    Oh sux. At least it would work tho..
     
  4. DanTheBanjoman Señor Moderator

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  5. mosheen

    mosheen

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    i'm not too sure about that, depends on the game.

    performance will be higher than 2x 4850.

    EDIT : Crossfire types
     
  6. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    Nope. That is wrong. CrossfireX now clocks the cards independently, so it will be a 4870 and a 4850. Not going to lose the performance edge of the 4870 at all UNLESS you go with a 1GB 4870 and a 512MB 4850.

    @ Mosheen

    Technically, that has no correlation to clock speeds to determine whether or not a 4870 downclocks to 4850. Useful info though.
     
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  7. inferKNOX

    inferKNOX

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    I want to quad crossfire a 4890 (1GB) + 4870 (1GB) + 2x4850s (512MB ea.), with a 650W PSU & 600W PSU. How does one setup the PSUs so that they startup together?
    I wanted the 4890 + 1x4850 + system on the 650W and the 4870 + 1x4850 on the 600W.
    And what would the... performance (I guess) be like, will they all work on 4850 level or what?
     
  8. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    You will be limited to the 4850's 512MB EDIT: If you were to omit the 4850's you would have 1GB available. Also, you will need to splice both power supplies' PWR ON (green) and a GROUND (black) together, then lead them to the main 24 pin on the motherboard. So when you turn on the system it will start both power supplies simultaneously.
     
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  9. Flyordie

    Flyordie New Member

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    .... Clocks now all run seperate...
    HD4850+HD4870 in crossfire will put you between an HD4850 and an HD4870 Crossfire in performance. Each card performs at its stock rated clockspeeds.
     
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  10. inferKNOX

    inferKNOX

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    Ok, so if the 4850s are in, then they'll be the limiter coz of the 512MB, then if they're out the cards switch into the 1GB bracket, so they'll clock independently? So if on has 2x4850 that are 1GB ea. then, the crossfire will still run in the 1GB bracket and all the cards will clock independently?

    How does one go about leading the 2 power supplies to the 24pin on the mobo? Know of any play by plays anywhere, with pics?
    Thanks by the way.:toast:
     
  11. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    That is correct. You are very welcome. Ygpm about the dual power supplies. Don't want to take this thread too off-topic.
     
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  12. 1933 Poker

    1933 Poker New Member

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    I have a case which you will need that supports dual psu countermeasures and in comes with special adapters to enable the use of multipsu's
     
  13. inferKNOX

    inferKNOX

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    OK, thanks, although I thought 1933 Poker might be interested in knowing what might be necessary for quad crossfire in the even of not having a behemoth PSU, but if you want to know about it 1933 Poker, just say so.;)
     
  14. wolf

    wolf Performance Enthusiast

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    Are you sure JrRacinFan?

    http://www.legitreviews.com/article/1107/1/

    Maybe its just cos they are so new but 5850+5870 = 5850 CF performance, minus a teeny tiny bit, prolly about 1% or less it seems.

     
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  15. inferKNOX

    inferKNOX

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    Oh really? I'd really love to see a pic of that adapter if possible, thanks. I know of cases that support it, but have never seen or heard of the adapters.
     
  16. wolf

    wolf Performance Enthusiast

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    inferKNOX says thanks.
  17. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    I am 110% positive. I'm pretty sure it's just driver maturity.
     
  18. inferKNOX

    inferKNOX

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    Last edited: Nov 11, 2009
    wolf says thanks.
  19. wolf

    wolf Performance Enthusiast

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    they made a button for that ;) heheheh

    no probs dude anytime.

    So Jr, you think after a few months of drivers me might see a 5850 and a 5870 Crossfired together, performing somewhere between 5850CF and 5870CF? that's interesting... Very interesting.

    *ponders*
     
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  20. ToTTenTranz

    ToTTenTranz New Member

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    You can crossfire any model within the same family and first performance-rating number (if the first two numbers are the same, you're good to go).


    This means 3850+3870, 4870+4850, 4650+4670, 4770+4750, and so on.
    The Crossfire system will only use the amount of memory available in the card with the lowest amount of memory available.
    If you do HD4850 512MB + HD4890 1GB, the graphics subsystem will only use 512MB. If you do HD3870 512MB + HD3850 256MB, the graphics subsystem will use 256MB.


    This happens because of the way Crossfire works. Most games run in Crossfire through AFR, or Alternate Frame Rendering.
    It consists in having both graphics cards rendering the exact same scene and alternating the ouptut of each graphics card.
    In a HD3870 512MB + HD3850 256MB setup, if you have a HD3870 512MB rendering frame 1, frame 2 will be rendered by HD3850 256MB.
    If the scene rendered by the HD3870 was occupying the 512MB, the same scene wouldn't fit in the HD3850's 256MB, so some textures would be missing. And because everything happens too fast, there's no time to flush textures (or polygon or shader data, whatever) from the main memory to the HD3850.
    So in order to maintain balance, the HD3870 512MB will only use up to 256MB, if being crossfired with a HD3850 256MB.




    These are the rules.
    There are some exceptions, though. Since they're identical, you can also mix the HD2600s with the HD3650 or the HD3850/70 with the HD2900XT/Pro. But the shader compatibility will be scaled back to DX10 (again the lowest factor).
     
  21. Wrigleyvillain

    Wrigleyvillain PTFO or GTFO

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    Thanks. Finally a simple and sensical explanation of the "memory halving" situation with cards with differing amount of vram. Knew there had to be one just never came across before. Would have loved to keep one of my 4850s with my 4870 1GB but they were only 512s and I needed more VRAM for 1920x1200.

    So this is not the case with SLI? Now curious...
     
  22. 1933 Poker

    1933 Poker New Member

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    It's actually the truth there. Although it is not supported on Vista that's all.
     
  23. 1933 Poker

    1933 Poker New Member

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    Basically the adapter connects the two ATX powercables together on the mobo so it's all in sync I guess, it doesn't actually draw full ATX power from both only taking from one of the ATX power cables the two connected ports that I saw.
     
  24. Jansku07 New Member

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    asdfdasf.jpg

    /thread :)
     
  25. inferKNOX

    inferKNOX

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    Huh? I'm not following, what's not supported in Vista, quad crossfire?
    Thanks for the help, but I'm afraid JrRacinFan & wolf beat you to it.:ohwell:
    I have always understood the concept (have been a technician for decade, but am no modder... well wasn't anyway, but things are changing;)), but never seen a... efficient way to splice the slave PSU upon boot w/o having to manually do it.
    It's my first time seeing the ATX extenders, never had seen a female ATX connector before today.
     

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