M vs : What's the Difference?

M2 SSD m 2 slot ssd 2 SSDs are keyed at both M and B positions, so they can fit in SATA slots and PCIe , even if they might not work in the latter NVMe SSDs are keyed only m2 sata vs nvme slot 2 specification identifies 12 key IDs on the module card and socket interface, but SSDs typically use three common keys: B, M, and B+M You

m2_1 slot 22 mm × 110 mm A size comparison of an mSATA SSD and an 2242 SSD B+M , 12-19 and 59–66, SATA, PCIe ×2, and SMBus Maximum