The slot says M.2, the drive says M.2, and they may still not understand each other. The notch in the connector decides.
The short answer
M.2 is a form factor and connector for small internal cards, not a speed grade. It can carry PCIe, SATA or USB, in many widths and lengths, and the notches (keys) in the edge connector tell you which interface a card is built for [1][2][6]. A code like 2280 gives the size: 22 mm wide, 80 mm long [3][5]. Our assessment: check size, key and interface before you buy, because "fits" and "works" are two separate questions.
How it works
- A form factor, not a protocol. SNIA describes M.2 (formerly NGFF) as a form factor for internally mounted SSDs that supports PCIe, SATA and USB. It is smaller than a 2.5-inch SSD and typically removable [2]. Many variants exist: up to four PCIe lanes, one SATA 3 port and one USB 3 port, with several connector and key IDs [6].
- The size code. The first two digits are the width, the remaining digits the length, both in millimetres. A Wi-Fi card can be 1630, an SSD 2242 or 2280 [3][5]. Every motherboard slot is 22 mm wide, even those that accept 30 mm wide cards [3][5].
- The key. Notches in the connector decide which slot a module fits. Key B carries SATA and PCIe x2, key M carries PCIe x4 and SATA, and a module with both notches (B+M) fits either kind of slot [3][5]. Keys A and E are used by Wi-Fi, Bluetooth and cellular cards [3][5]. The table below the steps lists the common keys.
- The key does not name the protocol. SATA drives tend to use B, and PCIe x4 drives use M, since only M offers four lanes [3][5]. A B+M module can be SATA, as Kingston puts it, but Dell notes that PCIe x2 drives can carry both keys too [3][4]. A SATA drive in M.2 still runs at SATA speed [3][4].
- Fits is not works. Different pin sets are connected on different boards, and a drive that physically fits a slot can still be a SATA drive in an NVMe-only slot, or the other way round. The board's manual lists the supported lengths and interfaces for each slot. For the protocol side see our entry on NVMe.
Keys at a glance
| Key | Typical use | Interfaces named by Dell and Ars Technica |
|---|---|---|
| B | SATA and PCIe x2 SSDs | PCIe x2, SATA, USB 2.0/3.0 and more |
| M | Fast PCIe x4 SSDs | PCIe x4, SATA |
| B+M | Compatible SSDs | Fits B and M sockets |
| A / E | Wi-Fi, Bluetooth, cellular | PCIe x2, USB 2.0 and more |
A practical example
You read "M.2 2280, M key, PCIe 4.0 x4, NVMe" on a drive page and "M.2 2280, PCIe, M key" in a board manual. Size, key and interface match, so it should work. Now the same drive for a mini PC whose manual says "M.2 2242, SATA only": it does not fit because of the length, and it would not be recognised either. This is a made-up example, because our inventory (as of 14 to 16 Oct 2026) holds no M.2 drive or slot data.
Checklist
- Read the size code (2230, 2242, 2280 or 22110) on the drive and in the manual.
- Compare the key of the drive with the slot, and note when a B+M module is offered.
- Confirm the interface: SATA or NVMe/PCIe, and how many lanes the slot is wired for [3][4][5].
- Check where the manual says a slot is shared or disabled, and whether it supports your drive length.
- Avoid A/E keyed Wi-Fi cards in an SSD slot and the other way round [5].
- Write down the model, key and interface before you order, so a return is rare.