Hero CrossHair x670E PCie Configuration Questions

[marcusob72]

Motherboard : ROG Hero CrossHair x670E PCie

Hi

Can anyone help with a few questions on PCIe configurations on the above motherboard please...

1. I want to use a 10Gbe LAN card in the 2nd PCIe Slot (X540T2 Dual 10GbE RJ45) - The card only requires PCIe Gen 3 x 8 lanes but if I plug it into the 2nd 16 lane PCIe Gen 5 Slot on the motherboard will the primary PCIe 5 x 16 Slot drop to 8 lanes ? If it will I presume this wont make much difference with a PCIe 4 4090, but it might when the PCie 5 5090 drops next year ? 

2. If I have all 4 M.2 slots with PCIe Gen 4 M.2 NVMe SSDs what impact does that have on the PCIe Gen 5 x16 primary GPU slot ? Does that drop to 8 lane, or it that slot only affected if I plug in the PCIe Gen 5 M.2 SSD Expansion card that came with the Motherboard ? 

Thanks.

[Jiaszzz_ROG]

Hello @marcusob72 

Thank you for reaching out to us.
1. The "Connectors with Shared Bandwidth" section of the ROG CROSSHAIR X670E HERO user manual states that PCIEX16_1 operates at x8 speed when PCIEX16_2 is in use. 

Therefore, if a PCIe LAN card is installed in PCIEX16_2, it may reduce the speed of the GPU in PCIEX16_1. 
Whether this affects your setup would depend on your specific use scenario.
2. In the same section, there is no indication that the M.2 slots share bandwidth with PCIe slots. 
Thus, even with all M.2 slots occupied by SSDs, the PCIe lane speeds remain unaffected. 
However, if you install a PCIe 5.0 M.2 card in the PCIEX16_2 slot, PCIEX16_1 will also operate at x8, as noted in the first point.

Thank you.