What is the difference between PCIe GEN 1, PCIe GEN 2, and PCIe GEN 3?

You can see that many mining operating systems suggest that you set your GPUs to PCIe GEN 2 in BIOS. You might have asked yourself already why exactly 2.

PCIe GEN setting is directly connected to data transfer rate and bandwidth. Cryptocurrency miners are usually using X1 slots on motherboard to connect the risers and because of X1 has special characteristics for different PCIe settings, these settings can also affect the hashrate and performance of your GPUs.

X1 slot's maximum speed on GEN 1 is 250 MB/s and this means that this is not large enough speed properly read and write DAG file size, which is for ETC now above 3 GB. So consequently, the hashrate dropped for PCIe GEN 1 and PCIe GEN 2 was required to use.

X1 slot's maximum speed on GEN 2 is 500 MB/s bandwidth, which is more appropriate for ETC mining.

Then you also have PCIe GEN 3 and GEN 4, which are currently unnecessary until PCIe resize bar support will be more common and not dedicated only for Ryzen motherboard. When this happens, the 1 GB/s to 2 GB/s will be possible to use with higher GEN settings.

If you would switch to PCIe GEN 3 now already, then you wouldn't be able to use as many GPUs as this would give more bandwidth to the X1 slot than what X1 slot needs for operating. Other slots wouldn't be able to load the GPU or the slots would take up more power (which wouldn't be seen on the driver's side - so on your minerstat dashboard - as this is the power that is consumed by risers and motherboard and not by the GPU).

If you are using spliiters, then you will probably need to set PCIe GEN 3 or PCIe GEN 4.

Motherboards don't report if you are using GEN 1, 2, or 3, but they report the bandwidth that is used. From this bandwidth we are trying to calculate which PCIe GEN setting you use and since not all motherboards fit all bandwidth values in the same way, we can miscalculate this. If you are sure that you have set PCIe GEN 2, you can ignore the message by diagnostic.