SLI on x16 and x8 pci express?

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I have a GA-z77x-ud5h and it is SLI compatible even though it only has 1 x16 PCIE slot and the other is running at x8.... How is this possible?? I'm thinking of buying another 680 but will I really see a performance boost? I thought you needed 2 pcie slots running the same speed to ski cards... Thanks
 
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MrAcd

MrAcd

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Feb 21, 2013
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No you are just fine, it will make little to no difference, and crossfiring gtx 680's are beast just make sure your PSU can handle it, the x8 will not run as fast but not enough for you to notice
 
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vmem

vmem

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Feb 17, 2012
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it is possible as you can run SLI at x8 speeds just fine historically. it was only with the most recent generation of video cards that we started saturating PCIe2.0 x16 bandwidth. also, you don't need the two slots to be running at the same speed, your computer will adjust it. ultimately, the two cards will be running at x8 speeds max (just how SLI rendering works)

since your board is a z77 series, it's fine to run a 680 in SLI at x8 on PCIe 3.0. I'd wager that you would at most see a 1-3% performance drop compared to someone running both cards at x16.
 
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ubercake

ubercake

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Oct 28, 2009
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If the motherboard is SLI-ready, it will come with an SLI connector and you'll have no problem with the 2nd 680 whatsoever. SLI requires x8 speed at a minimum. You will see no performance hit. With your board, when the 2nd PCIe 3.0 x16 slot is populated, both PCIe 3.0 x16 slots run in x8 mode (x8/x8). From the Gigabyte description of your motherboard at http://www.gigabyte.com/products/product-page.aspx?pid=4139#sp:

1) 1 x PCI Express x16 slot, running at x16 (PCIEX16)
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot.

2) 1 x PCI Express x16 slot, running at x8 (PCIEX8)
* The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode

In other words, both slots run at x8 when you pop the second 680 in. This will work fine.
 
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Guest

Guest
Thanks guys, that makes sense now. So is it safe to say that I will see a performance boost if i decide to SLI these bad boys?? Looking for a good performance boost not a 10fps performance boost btw
 
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ubercake

ubercake

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Oct 28, 2009
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With some games, performance nearly doubles. SLI is great tech.
 
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