Question PCIe versions and lanes speedj

[Sharpman85]

I have a question about PCIe lanes speeds with regard to backward compatibility. I want to build a X570 Ryzen PC but the motherboard I choose (Asus Rog X570-i) will likely share the GPU with the back ssd port. My question is as follows, when I install an nvme ssd and a GPU will the speed remain at the level of PCIe 3 x16 when it’s used in a PCIe 4 port or will it be lowered to PCIe 3 x8 as only 8 lanes will remain. I understand that it may be somewhat confusing to understand but it’s very important to understand this before I decide what to buy. The motherboard configuration is based on the previous X470 and B450 ones.

Thanks

 

[13thmonkey]

you need to wait for the specs to be fully released. My understanding is that the CPU has 4 PCI lanes for storage, and the PCH has 4 lanes for storage, so I can't see why they'd use any of the GPU lanes. Anandtech has an article of X570 as we understand it at the moment.

 

[Sharpman85]

you need to wait for the specs to be fully released. My understanding is that the CPU has 4 PCI lanes for storage, and the PCH has 4 lanes for storage, so I can't see why they'd use any of the GPU lanes. Anandtech has an article of X570 as we understand it at the moment.

Do you know how it works for PCIe 3 when only 8 lanes are available and a PCIe 2 device is used? I did not find any information on this when looking at the X470-i and B450-i motherboards.

Edit:
I mentioned on using the GPU lanes as Asus did exactly than with the older itx motherboards - if a second storage device is used it will use 8 of the GPU lanes, not the chipset ones. If they change it this time to PCH then that would be best, but I still would like to know how it works for older devices.