HD 4870 Crossfire performance on P965 Platinum

Hi all, i have a P965 platinum mobo and i want to go with 2 HD 4870 radeons in crossfire.
the only thing i am concerned with is that the P965 platinum mobo only support x16/x4 PCI express lanes when in crossfire configuration.
So my question is, will 2 4870 in crossfire on this mobo be seriously bottlenecked and give me poor crossfire performance?
Or will the crossfire bridge give enough bandwidth so the x16/x4 pci lanes are not that important?
thank for all info

Regards Peter
6 answers Last reply
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  1. The answer is yes.

    See how much pcie2.0x8 bottlenecks the less powerful 4850:
    http://www.tweaktown.com/articles/1472/7/page_7_benchmarks_crysis/index.html

    The x16 first lane will be bottlenecked by the x4 second lane, effectively make them both x4 lanes.
  2. Hello and welcome to the forums mate :)

    http://www.tomshardware.com/forum/245454-33-crossfire-faqs

    A note about Motherboards:

    Some Motherboards support Multi-GPU Technology at Dual 16x mode, some support it at Dual 8x mode and some support it at 16x 4x mode, what are the differences?
    Well for getting the best performance out of Multi-GPU cards,you need a Motherboard that supports Multi-GPU at dual(Or more) 16x mode like Nvidia 790i ULTRA SLI, Nvidia790i SLI, Nvidia 780i SLI, Nvidia 680i( As i said, NVIDIA 790i ULTRA SLI ,790i SLI ,780i SLI and 680i SLI support 3-Way SLI too),Nvidia 590i SLI, Nvidia nForce4 SLI 16x, ATI CrossFire Xpress 3200 or Intel X38 chipsets.

    Dual 8x is a very good configuration too,it doesnt have alot of difference with Dual 16x and its cheaper too.
    Chipests like Nvidia 750i SLI, Nvidia 650i SLI,NVIDIA 570i SLI, NVIDIA nForce4 SLI, ATI Radeon Xpress 200, Intel 975x and ONLY 2 Intel P35 boards(ASUS BLITZ FORMULA and ASUS BLITZ EXTREME) support Multi-GPU at dual 8x mode.

    However,there are some expections too,for example EVGA has a 750i Motherboard(The model of it is
    EVGA 750i SLI FTW)Which supports SLI at dual 16x mode unlike many 750i Motherboards which support SLI at dual 8x mode.

    The last one is 16x 4x, this one is the weakest and doesn't perform very good compared to dual 8x or dual 16x,so i won't recommend it for Multi-GPU configuration. Intel P35 and P965 chipsets support Multi-GPU at
    16x 4x mode.

    http://www.anandtech.com/video/showdoc.aspx?i=2837
  3. Just wait for the 4870X2 which will get you around your problem, be cheaper than 2 x 4870s and will be faster too.

    No brainer.
  4. Sorry for the silly question here, but I need to know. I have an SLi board (16x16) and was planning on running dual 8800GT's (got one and was gonna buy another) for good price/performance.

    Now obviously that has changed to wanting 2x 4850's. My question is, do you need a crossfire board in the same way that SLi requires an Nvidia chipset, or will an SLi board run crossfire too?
  5. americanbrian said:
    Sorry for the silly question here, but I need to know. I have an SLi board (16x16) and was planning on running dual 8800GT's (got one and was gonna buy another) for good price/performance.

    Now obviously that has changed to wanting 2x 4850's. My question is, do you need a crossfire board in the same way that SLi requires an Nvidia chipset, or will an SLi board run crossfire too?


    You need an intel board (I'd make sure to go for X38 or X48 for 16x16) to run Crossfire. Nvidia boards support SLI but do not support crossfire. In your case it wouldn't be a bad idea to just get another 8800GT and SLI them rather than have to get a whole new MB as well as 2 video cards.
  6. Thanks for the clarification. I suppose its not that bad, maybe they will make 4850x2's and I can just slap one of those in.

    Won't hold my breath though.

    My monitor only goes up to 1680x1050 anyway. no real need for a monster solution. Yet I still dream.
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