Question PCIEx16 drops to x 8 when M2 SSD is installed???

[Fakum]

I am looking to build a new PC with a 4090 GPU and an M2 ssd (and also considering it to support M2 Gen 5 for future upgrade). I am looking at the specs on a couple of Gigabyte boards and there are notes in there that I dont understand:

GIGABYTE Z790 AORUS Xtreme & GIGABYTE Z790 AORUS Master :

"1 x PCI Express x16 slot, supporting PCIe 5.0 and running at x16 (PCIEX16)
* The PCIEX16 slot shares bandwidth with the M2C_CPU connector. The PCIEX16 slot operates at up to x8 mode when a device is installed in the M2C_CPU connector.
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot. "

Does this mean that if I install a 4090 into the PCIEx16 slot it drops down to x8 if I install an M2 SSD? Or is this typical for all boards anyway? How do I avoid any performance drops (If any) using these parts?

Thanks

 

[Fakum]

Man! Im going to have to recheck my understanding of this. I thought (based on the video I posted) that all of the "E" (Extreme) boards had level 3 support in that they could literally support GEN5 devices in both slots simultaneously, and my interpretation of that is that there shouldn't be any drop down of speeds etc.

 

[CP5670]

No, it's very board dependent. They have 4 slots but often one or two are shared with something else. For this board, it seems having something in the fourth M.2 slot and fourth PCIE slot drops both to 2x, regardless of what PCIE gen the devices are. Similar things can happen with SATA as well.

 

[Fakum]

Ahhhh,, I thought you meant you were using PCIX-16 slot for GPU and the 1st M.2 slot for SSD and you were getting that effect.
The 2 boards I am currently eyeballing do not share any M2 slots with the 1st PCIEx16 slot from what I determine from the manual.

ASUS ROG Strix B650E-F Gaming:


MSI MAG B650 Tomahawk :