Question Using all 5 PCI-E Slots in Motherboard

[braxus]

I am running a Gigabyte X299 Gaming 7 motherboard. I have 1 video card installed in a PCI-E slot. The remaining PCI-E slots are being used for other cards like extra SATA ports with PATA connections as well, a 1394 card, an Intel PCI-E Optane drive, and a video capture card. Thing is I can't use all 5 slots at one time it seems. I had to remove 1 item because the computer wouldn't read the device when all 5 slots were used. Moving it to a different slot and leaving one empty works. I am using a 7800X CPU. Could this CPU be the reason why I can't use all 5 slots? I am also running a M.2 SSD as well, though the other 2 M.2 ports aren't being used. If I upgraded the CPU, would all 5 ports become active? Or is there an actual fault with the motherboard?

 

[MasterMadBones]

The i7-7800X supplies up to 28 PCIe lanes. The GPU and 2 SSDs already use 24 of those lanes. The remaining devices may use 1 or 4 lanes each, and I suspect the Firewire and SATA cards both want to use more than one lane in order to provide full bandwidth. Normally the CPU decides to cut the number of lanes going to the GPU. Because there is demand for so many lanes, the GPU may actually have to be cut down to just 4 lanes, which it may refuse. This could force the CPU to disable one of the PCIe connectors entirely. Upgrading to a 7900X or higher or any 9th generation X-series CPU will give you 44 PCIe lanes, likely solving the problem.

I would normally recommend you to try running your pc without the dedicated graphics card and occupy all PCIe slots to make sure the issue isn't caused by the motherboard, but since Skylake-X doesn't have an integrated GPU, that's impossible to check. So for you the advice either upgrading the CPU or learning to live with it (or replacing the mobo but that is extremely unlikely to change anything).