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At many motherboards there is M2 (key B) connector. This connector support several interfaces: PCIe ×2, SATA, USB 2.0 and 3.0, audio, UIM, HSIC, SSIC, I2C and SMBus.

But as I understood, all of these is possible functionality and motherboards could support only SATA or PCIe e.g., but not USB.

Is that correct that if the motherboard had M2 (key B) I can say that it requires USB interface support (at M2)? If it's not, by your experience, how many motherboards with M2 (key B) support USB?

j e
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    Depends on the keying, https://en.wikipedia.org/wiki/M.2#Form_factors_and_keying ; in this case, reading wikipedia actually answers your question: they are not "possible", they are mandatory if you use that specific keying. – Marcus Müller Oct 28 '21 at 16:07
  • “ … It is up to the manufacturer of the M.2 host or device to select which interfaces are to be supported, depending on the desired level of host support and device type… “ https://pinoutguide.com/HD/M.2_NGFF_connector_pinout.shtml So, it is actually up to manufacturer? Really? – j e Oct 28 '21 at 19:24
  • what that means is your manufacturer can choose which keying they want. If they choose B, they need to be fully B. – Marcus Müller Oct 28 '21 at 19:26
  • But there is no something like a standard? I can’t fully trust for such formulation. I can imagine, how many vendors can reduce several interfaces (to support usb3.0, 2.0, audio you need separate controller/cores) and set only required one (like sata or pci) just to move cost down. I understood you answers, and thank you very much, but I it still not clear. – j e Oct 28 '21 at 19:39
  • ok, how many times do you want me to repeat what I said? Because, if it's B-keyed, it's to signal it supports all the modes of B. Full stop. (everything else would make no sense- why using keying if it doesn't tell you anything.) – Marcus Müller Oct 28 '21 at 19:44
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    @MarcusMüller: I can assure you that there are a huge number of M.2 hosts that don't support all the interfaces corresponding to their keying. For example just about every USB SSD enclosure supports only SATA SSDs. Keying still has value under the rule that no pin is used in any way different from what the keying dictates. That ensures that mating a host and device with the same keying does not cause damage. It's still possible that a large number of the pins are not used at all by a particular host or device. – Ben Voigt Oct 28 '21 at 21:37

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