I bought a used R5E10 X99 Motherboard with a i7-6900k CPU in order to run quad GPUs.
Specs say I should be able to run 3.0 x16/x8/x8/x8 or even x8/x8/x8/x8 (either would be fine), and the 6900k has 40 PCIe lanes to support it.
The issue is, the last slot (PCIEX8_4) only runs at PCIe 2.0 x1. *In the BIOS, i tried both options Auto (x8/x8/x8/x8) and setting it to x16/x8/x8/x8. *Same result for both options. *I understand that slot shares lanes with the U2 and M2, but the BIOS option says it will disable them if set to run the main slot at x16.
To troubleshoot, all I boot up with only one GPU in the PCIEX8_2 slot (x8 max) and card gets recognized in BIOS as x8 in GPU Boot.
Take the same card and plug into the PCIEX8_4 slot, and the card doesn't show up in BIOS (says No VGA Card), but it will show up in windows and display video. But GPU-z states it's running at PCIe 2.0 x1.
*Another strange thing, is that if i turn off the PCIe lane using the dip switch for PCIEX8_2, the GPU will not show up in windows as expected. *But if i turn off the switch for PCIEX8_4, the GPU still shows up in windows at the reduced speeds.
Tried many BIOS settings, CSM, 4G Encoding, explicitly setting the port to Gen3, going back one BIOS version...nothing makes a difference. *
I would think the BIOS would recognize the GPU in the slot in GPU Boot, regardless of it's speed. *The "No VGA Card" showing up worries me there's an issue with the board, but it still displays video fine thru it so that part is confusing...
Appreciate any help, thanks!
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