A Short Discussion on NGFF M.2 NVMe

There is so much confusion over M.2 SSDs.

Articles that are quite well written and informative never seem to explicitly state what the real world implications of a B-Key, M-Key, and B and M Keying is.

The first thing to remember that all the Keying has different implications for Sockets than it does for Devices (an SSD)

Important Items to Know

SSDs that fit into NGFF (Next Generation Form Factor, the old term) / M.2 (the new term) Sockets come in two "flavors": NVMe (Non Volatile Memory eXPRESS, which is newer) and non-NVMe (sometimes referred to as NGFF SSDs)
Both NVMe and NGFF SSDs can support USB, SATA / AHCI, and PCI-E (2 Lanes for NGFF and 4 Lanes for NVMe)*
Sockets that are M Keyed require an NVMe SSD

* Notice that the word can is in italics. This means a socket or device can support those protocols, it doesn't mean that they do.

Sockets (and what the keying indicates)

B-Key: Only supports SATA / AHCI (not PCI-E 2 Lane or 4 Lane) and USB
M-Key: Supports PCI-E, SATA / AHCI, and USB
B and M Key: There doesn't seem to be a socket that is keyed B and M

Devices (SSDs)

B-Key: Can / Has the potential (If implemented by the manufacturer, but not required to be implemented) for SATA / AHCI, PCI-E 2 Lane, and USB