What is the meaning of the keys of M.2 SSDs?

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Question

What is the meaning of the keys of M.2 SSDs?

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Answer

Depending on which interfaces are provided by a M.2 connector, a specific form of the connection is used. These so-called keys require M.2 plug-in cards with recesses at certain points, so that only suitable plug-in cards fit into the respective M.2 connectors.

Most currently available M.2 SSDs are Key B + M. They have both recesses and can be plugged into Key-B as well as Key-M connectors.
Buyers need to make sure the connector and module support the same key otherwise the M.2 card will not fit.

Quelle: wikimedia.org / NikNaks / CC BY-SA 3.0
M.2 can provide both SATA and PCI Express as an interface:

• Key B: PCIe ×2, SATA
• Key M: PCIe ×4, SATA

Overview of the maximum speeds of different interfaces

As mentioned above, M.2 can provide both SATA and PCI Express as an interface.
M.2 SSDs connected via PCIe offer a speed advantage.
PCIe 2.0 allows 5 GBit/s per lane, PCIe 3.0 allows 8 GBit/s per lane.

Interface	Maximum speed
SATA 3	6 GBit/s
PCIe 2.0 x2	10 GBit/s
PCIe 2.0 x4	20 GBit/s
PCIe 3.0 x2	16 GBit/s
PCIe 3.0 x4	32 GBit/s
PCIe 4.0 x4	64 GBit/s

References:

General Technical Knowledge Base: M.2

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The information in this article refers to:

• M.2 SSDs

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Review Date: 2022-11-15