Your current arrangement is causing some uncertainty—let’s explore ways forward together.
Your current arrangement is causing some uncertainty—let’s explore ways forward together.
It seems you likely left all the slots in Auto BIOS enabled, but Asus boards aren't very intuitive when you skip others. They can switch to an x16 setup and turn off the rest. Try adjusting manually so the first slot is PCIe Gen 3 x16 and disable the remaining ones. Also, press the question mark and rerun the PCIe test—sometimes it freezes and shows incorrect data.
The article was discovered on the QuantumSingularity forum. It discusses the AMD 500-400 series crosshair VII M drive and its impact on PCIe bandwidth.
It seems there may be an issue with your motherboard or graphics card, since both should work smoothly in a PCIe Gen3 x16 setup. If you follow the advice in the comment below, some users have reported success by running both M.2 slots with their cards still using x16 configuration. Try reinserting the GPU, as this could also be the reason.
Explored deeper into the guide and noticed they avoided highlighting the drawbacks of their product upfront. Later, the document mentioned: If this is the intended version, it explains why it operates in x8 mode—it’s clearly a questionable decision by Asus. The main concern now is whether this restriction stems from the older Ryzen 3000 chips due to fewer PCIe lanes (16) and if it will function properly with the 5000 series where the count rises to 20. It’s still feasible that adding a 5700X3D or 5800X3D could unlock the extra four lanes if the BIOS settings are adjusted correctly.
The issue lies in the CPU generation gap being exactly what’s required for the motherboard to operate correctly. The 3900X supports 16 PCIe lanes, whereas the 5800X3D and 5700X3D offer 20 lanes. In principle, this should enable the board to run in x16 mode with both slots filled after installing the new CPU. I’m unsure how Asus BIOS functions now, since I haven’t used them recently.
Obtain a 5700X3D or 5800X3D. Ensure you're using the most recent BIOS.
I’ll remember that thought, I’m going to take a closer look to see if I should just wait and decide.