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At what point does a 8x pci-e lane become a bottleneck?

Devrij

Devrij

Devrij

Soldato
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I'm running a P5Q deluxe, which has either a single 16x or dual 8x pci-e lanes, and I'm debating either adding another 5770 into the mix or saving up for a better single card (although selling my 5770 is a bit of hassle). I'm wondering: if I got a 5850 with the intention of adding another later down the line would it be limited by 8x lanes (in which case I'd be best going saving for a 5870/5970 to avoid this or going with the 5770cf and just having a major change of board/cpu/etc when I needed to) or is that a decent upgrade path? Thanks for your input :)
 
Devrij said:
I'm running a P5Q deluxe, which has either a single 16x or dual 8x pci-e lanes, and I'm debating either adding another 5770 into the mix or saving up for a better single card (although selling my 5770 is a bit of hassle). I'm wondering: if I got a 5850 with the intention of adding another later down the line would it be limited by 8x lanes (in which case I'd be best going saving for a 5870/5970 to avoid this or going with the 5770cf and just having a major change of board/cpu/etc when I needed to) or is that a decent upgrade path? Thanks for your input :)
Click to expand...

That's PCIe 2.0 I believe ... I lost about 1.5 fps (from 71fps) running 16x, 8x compared to 16x, 16x for Xfire 5970+5870 so that might give you an idea ...
 
Multi GPU cards will become bottlenecked.

Every single GPU card will experience at max 3% FPS loss IIRC.

Your 5770's will be fine :) and 5850's will be grand as well.
 
So besides scaling issues, if I ran two 5870's (theoretically) on 8x,8x I'd only lose a few frames? And yeah, it's pci-e 2.0
 
As far as I am aware you may loose a few (as in very few) frames per second. Not enough to make it worth changing your motherboard before you build a new base system.

Saying that, this isn't something that concerns me overly as I have been on a powerful single GPU card since having multiple GPUs became common, hence my knowledge on this is rather limited. I may break that trend and get another 5870 further down the line though.
 
It's not so much x8/x8 becomes a bottleneck it's just as important to have a good chipset that can manage multiple video arrangements. Have a read of this article their testing crossfired modest HD4850's on P45 x8/x8 against x16/x16 X48 boards, just look at how badly the P45 performs and it's not due to the x8/x8 bandwidth as more powerful cards like the HD5870's crossfire nearly as well on x8/x8 on P55 boards as it does on X58 x16/x16 (see on of the links above).

So the bottom line is if you plan on using crossfire on P45 you might wish to reconsider as the P45 chipset isn't good enough.
 
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