M.2_1 and PCIe Gen 5 x16

[magicnorm]

Need clarification so I can have the best results.

Knowing that:

PCIe Gen 4 x8 speed is 32GB/s

PCIe Gen 4 x16 speed is 64GB/s

PCIe Gen 5 x8 speed is 64GB/s

PCIe Gen 5 x16 speed is128GB/s

I have a Asus ROG STRIX Z790-E GAMING Motherboard and it has a PCIe Gen 5 x16 interface for the GPU.

I also have a RTX4080 Super and it has a PCIe Gen 4 x16 interface.

The motherboard documentation states that if I put a NVMe in the M.2_1 that shares bandwidth with the PCIe, the PCIe will drop to a Gen 5 x8.

Am I right thinking that putting a M.2 NVMe should not affect the GPU because the PCIe Gen 5 x8 speed is equivalent to PCIe Gen 4 x16 speed.

Thanks

[Jiaszzz_ASUS]

Hello @magicnorm 

Thank you for reaching out to us.
For specifications regarding PCIe 4.0 and 5.0, please refer to What Are PCIe 4.0 and 5.0?
Could you please confirm if your current motherboard model is the ROG STRIX Z790-E GAMING WIFI or the ROG STRIX Z790-E GAMING WIFI II?
After consulting with the relevant member, we have confirmed that when you install a PCIe 4.0 x16 graphics card in the ROG STRIX Z790-E GAMING WIFI's PCIe 5.0 x16 slot, it will only operate at PCIe 4.0 x16 speeds.
Additionally, if you install an SSD device in the M.2_1 slot at the same time, causing the bandwidth to drop to x8, the graphics card will then run at PCIe 4.0 x8, which equals 16 GB/s.
Therefore, we recommend installing your PCIe 4.0 x16 graphics card in the motherboard's PCIe 4.0 x16 slot to ensure it runs according to specifications.

Thank you

[magicnorm]

Hi,

I have the ROG STRIX Z790-E GAMING WIFI II card.

Just to clarify, installing an SSD device in the M.2_1 slot, will cause the bandwidth to drop to x8.

But will it drop to a PCIe 5.0 x8 speed or a  PCIe 4.0 x8  speed.

I am asking because if it drops to PCIe 5.0 x8 speed it would equal to PCIe 4.0 x16 speed.

[Jiaszzz_ASUS]

Hello @magicnorm 

Thank you for the reply.
As I mentioned in my previous response:

we have confirmed that when you install a PCIe 4.0 x16 graphics card in the ROG STRIX Z790-E GAMING WIFI's PCIe 5.0 x16 slot, it will only operate at PCIe 4.0 x16 speeds.
Additionally, if you install an SSD device in the M.2_1 slot at the same time, causing the bandwidth to drop to x8, the graphics card will then run at PCIe 4.0 x8, which equals 16 GB/s.

When you install a PCIe 4.0 x16 graphics card in a PCIe 5.0 x16 slot and the M.2_1 slot is occupied, the graphics card will operate at PCIe 4.0 x8 speed.

Thank you.