What are the performance differences between PCI-Express x16 and x4

Posted by Cestarian on Super User See other posts from Super User or by Cestarian
Published on 2014-06-10T08:11:46Z Indexed on 2014/06/10 9:28 UTC
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Filed under:

graphics-card

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motherboard

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pci-express

I have two PCI-Express 2.0 x16 slots on my motherboard, but one of them is actually just x4.

For passing through my graphics card to a virtual machine I need to use both slots simultaneously and unfortunately, the easiest way for me to achieve that is putting the stronger card in the x4 slot (secondary slot; I need the stronger card to be in the secondary slot, not the primary).

As such I am wondering what sort of noticable performance differences I can expect from using the x4 slot with a strong card as opposed to having it in the true x16 slot. Does it limit the performance so much that the strong card in the x4 slot will actually perform worse than the significantly weaker card in the x16 slot? (For spec comparison I am using a GTX-670 in the x4 slot and GTX-550-Ti in the x16 slot)

What implications does this have?

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