NVMe vs : Bus, Interface, and Protocol

is a new form of connectivity that allows a SSD to connect directly to the PCI-E bus rather than going through a SATA controller By

I currently am using a Pi 5 and I have connected via a Blue USB slot an External SSD enclosure, with an PCIe Gen 4 NVMe SSD in it I know the PCIe

nvme slot 2 drives are “keyed” at one end so as to prevent the end-user from inserting them in an incompatible socket PCIe NVMe drives are 'M' keyed SATA ones,

nvme in pcie slot 2 NVME SSDs with a notch is the strongest; from the compatibility, M 2