4 PCIe Slot Facts About the ASUS PRIME B550M-A

The primary x16 slot runs at PCIe 4.0 x16 directly from the CPU, giving your GPU full Gen 4 bandwidth.

The second x16 slot drops to PCIe 3.0 x4 through the chipset, so don’t expect Gen 4 speeds there.

Two PCIe 3.0 x1 slots handle smaller add-on cards like Wi-Fi or sound cards.

This is the standard B550 layout: Gen 4 where it matters for the GPU, Gen 3 everywhere else.