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Question about pci-e slots

Last response: in Graphics & Displays
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February 25, 2012 4:31:25 PM

Now i have a very simple question and i'll use numbers to hopefully make it easier to understand. They are not real numbers of any kind, just a representation

Now lets say a mobo has 2 pci-e 3.0 slots single at x16 and dual at x8
Now lets say i have video card that can have a score of 1000 at x16 and by that logic 500 at x8

So that 1 video card can have a score of 1000 by itself.
Now if i bought a 2nd exactly like it, and ran them both, both being at x8, then each one would be at 500 to a total of 1000? :heink: 

Is this how the single/dual works? So i actually cannot increase performance by having two cards so what the point of it be?

And then if i have 2 x16 slots, and ran two of them together to get a score of 2000, is that how it would work? :heink: 

Thanks for your help

More about : question pci slots

February 25, 2012 4:35:10 PM

This is how it would work if PCI-e bandwidth were the major limiting factor of graphics card performance. However, this is not the case. No single card is bandwidth limited on PCI-e 2.0 x16. Therefore, no single card is going to be limited on PCI-e 3.0 x8.

So, you could crossfire some 7970s on a PCI-e 3.0 setup, with both running in x8 mode, and have basically no performance loss compared to two cards running in PCI-e 3.0 x16. Even in PCI-e 2.0 x8 with two cards, you're going to see very minimal performance loss (and I'm thinking about 2x7970s here - you wouldn't see any loss on midrange cards).

PCI-e bandwidth really isn't a limiting factor on GPUs.
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February 25, 2012 4:52:11 PM

Ok, thank you very much, that was very informative and helpful.
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February 25, 2012 5:07:06 PM

This may be dated information. My understanding is Crossfire runs well even on 16x/4x Crossfire (provided the 4x is not compromised by shared usage).
SLI is reputed to require 8x/8x for proper performance.

There is a toms article on scaling with AMD vs Nvidea GPUs with AMD vs Intel CPUs, if memory serves.
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February 25, 2012 5:41:08 PM

Ok, i will see if i can find those
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