Issue with ROG Crosshair X870E Hero Running PCIe 16x at 8x

[quantumfield]

I'm have an issue with my MB (Crosshair X870E Hero) running the top PCIe 16x running at 8x.  I'm using only the top PCIe slot, PCIEX16(G5)_1 (for GPU), and have an nvme drive on m.2_1 and m.2_2.  I have absolutely nothing on m.2_3.  So, per the manual, PCIEX16(G5)_1 should be running at 16X, not 8X.

From the Motherboard Manual

 Here are my system specs:

CPU: Ryzen 9950X3D
GPU: Astral RTX 5090
Storage: Sumsung 990 Pro nvme (2 TB on m.2_1 and 4 TB on m.2_2)
RAM: 64 GB
BIOS (Latest): 1504, 05/28/2025

Any help that anyone can provide would be very much appreciated.  Thank you!

[Jiaszzz_ROG]

Hello @quantumfield 

Thank you for reaching out to us.
Based on your description and referring to page 15 of the user manual under “Connectors with shared bandwidth”:

When a GPU is installed in PCIEX16(G5)_1 and the M.2_2 slot is occupied, the system will follow Configuration 3. In this case, even if M.2_3 is left unoccupied, the GPU will operate at x8 bandwidth.
For the GPU to operate at full x16 bandwidth, it must be installed in PCIEX16(G5), while PCIEX16(G5)_2, M.2_2, and M.2_3 all remain unoccupied.
We recommend reviewing the user manual once more to verify your current hardware configuration.

Thank you.

[quantumfield · Accepted solution]

Thank you for this.  I moved the second nvme drive to M.2_5 and now PCIEX16(G5)_1 is now properly running at 16 x 5.  With that said, the written instructions could do with some clarification, namely stating that "When M.2_1 is enable, and M.2_2 or M.2_3 are enabled, PCIEX16_1 will run x8, and PCIEX 16_2 will run at x4."