Asus motherboard question

[Drifter104]

Reading the manual for the ASUS ROG STRIX X670E-E am I right in thinking that if I want to run 3 m2 drives without dropping down to x8 on the PCIe 5.0 I would need to run them in M2_1, M2_2 & M2_4?
I'm a bit confused as the manual states if you use M2_3 the PCIe5_1 drops down to x8 and the _2 drops to x4, but there is also a table that implies if a PCIe card is used in slot PCIe_2 then PCIe_1 is dropped down to x8. Would that not also apply if something is in M2_2 slot?

 

[Drifter104]

My understanding is:

M.2 slot 4 comes off the chipset and is always PCI-E 4.0.

The CPU has 24 PCI-E 5.0 lanes.

M.2 slot 1 and 2 use the spare 8 lanes (four each).

The primary PCI-E slot uses the other 16 lanes.

M.2 slot 3 shares bandwidth with the PCI-E slots (1 & 2), and since the CPU can only run 16 lanes OR 8 lanes (primary) and in this case: 4 lanes (secondary), the primary PCI-E will always drop to 8 lanes when M.2 slot 3 is used.

In summary:

You can only run 2 PCI-E 5.0 drives (slot 1 and 2) and 1 PCI-E 4.0 drive (slot 4), if you don't want to lose PCI-E lanes on the primary slot.

If you put a card in PCI-E slot 2 then the same rule applies as populating M.2 slot 3, since the CPU still has to switch to 8 lanes (primary) and in this case: 4 lanes (secondary).

That makes more sense than what I had come up with.

Thank you