Using GPU and sound card with a 16 lane CPU? How does mobo react?

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Aurora-Storm

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I'm specifically looking at the GTX Geforce 970 and the Creative Sound Blaster Zx. As far as I can tell a GPU is going to use all 16 PCI-E lanes, and the sound card will use one. Ideally you would plug the GPU into the first slot on the mobo (utilizing all 16 lanes) and then the sound card into the second slot, which would use a single lane. Except that's not how it works, because won't plugging anything into the second slot reduce both lanes to 8? Are there any motherboards out there that would actually be able to recognize that the second slot is using a single lane? Is that even computationally possible?
 
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popatim
As for the x8 x16 discussion; i'm hesitant to call it an issue; it will operate in x16 mode as long as nothing forces the cpu to drop it to x8 mode (like inserting a pcie card into the other x16 slot) BECAUSE the bandwidth of PCIE version 3 is so high that none of the new gpu's can fully use it which is why dropping it to x8 mode has very low impact, if any at all. A pcie v3 x8 interface is just shy of a ver2 x16 bus in terms of bandwidth. (7880MB/s vs 8000MB/s) IIRC V3 also removed some protocol overhead to bring it's performance above that of v2 despite it being slower
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Aurora-Storm

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Hmn, for some reason I thought that a GPU would be able to use all 16 lanes. Do you have any literature I can reference to? I've been doing a lot of reading/watching but I haven't come across that particular point.

If it's true that the 970 would only really be able to use 8 lanes anyway, that does save me from a potential jump in CPU price to make sure my cards work to their full potential.
 
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Aurora-Storm

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This is a fair point, thanks for the reply!
 
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popatim

popatim

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As for the x8 x16 discussion; i'm hesitant to call it an issue; it will operate in x16 mode as long as nothing forces the cpu to drop it to x8 mode (like inserting a pcie card into the other x16 slot) BECAUSE the bandwidth of PCIE version 3 is so high that none of the new gpu's can fully use it which is why dropping it to x8 mode has very low impact, if any at all. A pcie v3 x8 interface is just shy of a ver2 x16 bus in terms of bandwidth. (7880MB/s vs 8000MB/s) IIRC V3 also removed some protocol overhead to bring it's performance above that of v2 despite it being slower
 
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Aurora-Storm

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Jan 5, 2015
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So if I plug the sound card into a PCI-E x1 slot, a PCI-E x16 will or won't drop the GPU into x8? It's good to hear at least that the relative performance between x8 and x16 when GPUs are concerned is evenly matched.
 
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