The B+M keys on an M.2 SSD allow for cross-compatibility on various motherboards if the appropriate SSDs protocol is supported (SATA or PCIe). Some motherboard host connectors may be designed only to accommodate M-key SSDs, while others may only accommodate B-key SSD. The B+M keys SSD was designed to address this issue; however, plugging in a M.2 SSD into a socket will not guarantee it will work, as that will depend on having a shared protocol between the M.2 SSD and the motherboard.