4850 Crossfire bottlenecked by x8/x8 lanes

arcanus said:
I just pulled the trigger on my new system, including a P5Q PRO (P45) and 4850, with intentions to eventually grab another for some CF action. Looks like this was not the best choice ;/
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I'm still not convinced.
 
Also, for those of you that have p35 or p45 boards and are trying to run crossfire, you can play with overclocking your PCI-e bus. That can help overcome the limitation a bit.
 
Man, I can't ever see myself going with Crossfire, but to basically have the possibility eliminated because of a 4x slot on my P5K is disappointing. WTF was the point of having two slots then? Might as well have given me another PCI slot.
 
So that means using 4 of them in crossfire x on the current amd boards will be bottle necked and we prob won't see the true power of what they have to offer. that sucks.
 
So any current crossfire capable x38 or x48 mboard will have the ability to run crossfire at dual x16 pcie 2.0 correct?
 
I have to weigh in here as I have a p5q-e and a 8800gt overclocked. I am looking strongly at a 4850 CF setup in the near future... or 4870 CF upon another price drip :)
I haven't seen any damnable evidence of 8x8 vs 16x16 by a huge margin. If its less then 10% so what? if its 25% or more then...
 
TweakTown released really lame articles and reviews when the HD3XXX series came around.
They were the very first to review them, and in their charts, the performance was ridiculously under what we saw in every other review. They made the HD3850 look as weak as a 8600GT.
There was a lot of complaining and their foruns even got closed for a while because of people complaining about their lack of professionalism at the time.

Also if I remember correctly they were the first to review the 8800GT too and made them look more powerful than the 8800GTX 768 in every test, which was soon discovered not to be true after other reviews came around.
 
I agree that the Tweaktown results don't appear accurate to me.
Don't mean to crosspost threads, but I posted a link to a blog post I put together when I tested 2900XTs in crossfire on a P35 board (which offers 1/4th the bandwidth in the 2nd PCIe slot compared to P45). http://hardforum.com/showthread.php?t=1327138
In case you don't want to follow the links, I found increases of:
TF2: 73%
Oblivion: 64%
ET:QW: 50%
Crysis demo (before the multi-GPU patch came out): 40%

So, if the 2900XT could survive on the PCIe 1.1 x4 link, I'm pretty confident the 300% increase in bandwidth provided by the PCIe 2.0 x8 link in P45 could provide the 4000 series with adequate bandwidth.

Also, I tried to overclock the PCIe bus by 10% to 110mhz and tested 3dmark, and it showed a 5% performance increase. So, Pcie bus overclocking can help offset the limitation in some cases.
 
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