I was watching a video about the new X870E motherboards, and I have a question about PCIe lane sharing, especially when dual-booting with Linux.

Many X870E motherboards feature multiple Gen 5 M.2 slots (typically 1 or 2) that share bandwidth with the GPU. This means that if an SSD is installed in one of these slots, the GPU will run at x8 instead of x16.

To explain my question more clearly, let’s take the ASUS ROG Strix X870E motherboard as an example. Here’s the M.2 slot configuration (as per the official specs):

There are 5 M.2 slots in total.
The M.2_2 and M.2_3 slots share bandwidth with the PCIe x16 (G5) slot for the GPU. If either of these slots is occupied by an SSD, the GPU will run at x8 instead of x16.
The remaining M.2 slots don’t affect GPU bandwidth.

Now, let’s say I install Windows on an SSD in the M.2_1 slot (which doesn’t share lanes with the GPU) and Linux on an SSD in the M.2_2 slot (which does share lanes with the GPU).

If I boot into Windows, the SSD in M.2_2 (containing Linux) is not in use. Since the Linux SSD isn’t being accessed while I’m in Windows, will the GPU still run at x8, or will it run at x16?

My assumption is that the GPU will still run at x8, as the bandwidth sharing is a hardware limitation. I doubt that the motherboard can dynamically reallocate PCIe lanes based on whether or not an SSD is actively being accessed. What do you think?