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Discussion Starter · #1 ·
I have an older Abit AW9D-MAX mobo with the intel 975x chipset. It therefore supports 1x16 PCIE or 2x8 PCIE in crossfire.


I'm currently running a single HD5770 which I'm very happy with -it beats the pants off the old 8800 GTS 512 running in there previously (which was bigger; louder and more power hungry). After checking some reviews on running 2 of these cards together in crossfire it actually sounds like it could be a worthwhile upgrade.


My question is that given this is a PCIE 1.0 mobo and that the lanes are reduced to 8 when running both slots, am I likely to see noticeably lower performance scaling than what the published benchmarks indicate?


It seems to me that if I now have 2 cards I'm increasing the traffic on the PCIE lanes while at the same time halving the number of lanes available. I therefore can't help but wonder if this will result in a bottleneck that significantly castrates potential performance gains. Then again 2 5770's gives you about the same (or better) performance as 1 HD5850 so perhaps the total level of performance of 2 5770 cards is still not enough to saturate all 16 lanes, unless a single HD5850/70 can do that already?


In case it helps, I'm running a 2.6Ghz e4700 core 2 duo (native 800fsb) @ 1066fsb @ 3.45Ghz. (This was a modest and easy overclock to attain and I could probably go a lot higher if I wanted to be ambitious about it -the e4700 is an overclockers wet dream) I'm connecting to a full HD LCD @ 1080p


This system scores around 14K-15K on 3DMark 06 on default test settings (eg non registered version)


ps. Please don't tell me to upgrade the mobo -this is one of a number of PC builds I have lying around and is the result of cobbling together various spare parts into what has become a surprisingly well performing system. It's somewhat of a hobby for me and I'm more interested in whether anyone has some tangible insight into whether the performance bottleneck is likely to manifest in real world gaming conditions as my curiosity is peeked and I can't find any solid literature about it on the net. I think I may just have to get another HD5770 anyway just to satisfy my curiosity :)


Cheers
 

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Tomshardware has periodically tested the effects of reduced PCIE lanes on video cards. In general, performance is slightly degraded and only at high resolutions. This article , from 2008, includes the 975X chipset in it's comparison and concludes a 7.7% performance hit from operating 8x/8x.


Adding another 5770 to your setup will almost double its performance. Even minus the PCIE bottleneck you'll see a significant improvement.
 

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Discussion Starter · #4 ·
Thanks for that link, it was an interesting read.


I've never actually run a dual GPU setup before, in reality the high power requirements; extra noise have always turned me off the idea, but these particular cards offer a great combination performance at low cost; low power and noise. Running 2 actually seems like a reasonable proposition now that I already own one. ps. I'm running the Sapphire Vapor-X model, so it is extra quiet and cool. As a result it also overclocks amazingly well, and yet still doesn't get very hot.


Honestly, I've never been quite this impressed with a GPU before.
 
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