The difference between PCIe x1, x4, x8, x16 and x32

Bandwidth of PCIe · PCIe x16 : 128 Gbits · PCIe x1 — open stack: 8 Gbits · PCIe x16 : 32

An x4 PCIe device has a theoretical max transfer rate of MBsec according to wiki

pcie slot size MXH950 and MXH952 PCIe FireFly Optical NTB, Host & Target Adapter Adapter for IO, Server and workstation connections PCI Express x16 host port

pcie m2 slot It's a slot of x16 size but electrically x4 This