Asus X99-A PCI-E x16 default at x1, I need to know if I can change this

[Ov3rTheTop]

Hey everyone,

I just watched LTT's video on the limits of PCI-E lanes with 28 and 40 lane CPUs. Linus recommended checking the restrictions that some mobos might have due to limited lanes. So I checked the mobo I'm interested in, being the Asus X99-A, and found a weird thing. Here's what it says word for word in the specs:

 

 

 

The PCIe x16_2, PCIe x1_1 and USB3_E56 connectors share the same bandwidth. By default, the PCIe x16_2 slot and PCIe x1_1 slot will automatically run at x1 mode with USB3_E56 enabled for best resource optimization.

 

I checked images of the board and found that the USB3_E56 connectors are two of the rear USB3 ports which I don't really need considering all of my USB3s will be through front I/O thanks to the board's two USB3 headers. So the question I have is: Can I change it so that the USB3_E56 connectors are disabled allowing me to run dual graphics cards, will this be dealt with automatically by the board if I install a second card that wants all 16 lanes, or is something I'm stuck with?

 

Would love to hear if anyone has had experience with this. 

 

Also I'm looking at MSI's X99 SLI plus board as it has nothing like this in the specs. 

 

Thoughts?

 

Thanks!

[Hecknologist]

If you're wanting to run sli graphics cards the pcie slots only need to be 8x electrically for nvidia cards, and 4x electrically for amd(16x physically or you can cut a notch in the end of the slot for the connetor overhang). I'm not aware of a card that requires 16x gen 3 electrically. As for the question, you can disable specific plugs on your mobo through device manager or similar in the operating system, which should theoretically alleviate the reduction of available lanes. However I wouldn't buy a board on a hunch and would instead look for if the board officially supports sli/crossfire (being an x99 board I would assume so) as that will ensure the motherboard matches your use-case.

Hope this helps.