I know what you’re thinking, this isn’t possible! But…it kinda should be? The AsRock WRX90 WS Evo datasheet shows the two MCIO PCIe Gen5x4 ports as sitting on neighboring PCIe lanes on the same root port off the CPU so in theory it should be possible to hook them up to a single PCIe Gen5x8 device. Electrically you’d have to make sure to isolate the clock and reset signals on the second port, the usual splitter cables obviously don’t do this, but assuming you handled that and got the BIOS to cooperate (it seems possible this won’t happen without AsRock, but about 70% chance Claude can find a 0day in the BIOS to exploit…) what else would go wrong?
The only obvious issues to me would be that the two ports possibly have separate retimers, which might result in the second set of 4 lanes getting off, or that the traces for the separate port on the motherboard itself aren’t matched, leading to timing offset issues, but it still seems worth a try, assuming the BIOS cooperates.
