M.2 explained: keys, lengths and the common SSD sizes
M.2 is a compact SSD form factor with key notches and length codes. The key determines the interface and lane count, while the length code specifies the physical size. This article explains how to read M.2 specifications and choose a compatible drive.
What is the M.2 form factor?
The M.2 form factor is a compact card standard for solid state drives used in client and enterprise systems, as described in the SNIA SSD form factors guide. It replaces older mSATA and 2.5-inch drives in many applications, offering a small footprint and a direct motherboard connection.
M.2 drives can use either the SATA or NVMe protocol. The physical card has an edge connector with key notches that prevent insertion into incompatible slots.[](https://wikissd.pages.dev/pcie-lanes-nvme/)
According to KIOXIA's business SSD category comparison, client SSDs use M.2 2230, 2242, and 2280 sizes, both single-sided and double-sided, while data center and enterprise drives use larger E1.S and E3.S forms.
Keys: B and M
The key is the notch on the card edge that decides which slots accept the drive. Samsung's internal SSD installation FAQ explains that a B-key enables SATA or NVMe with up to 2 PCIe lanes, while an M-key enables NVMe with up to 4 PCIe lanes.
Many M.2 slots are M-key only, which supports PCIe x4 for the highest speed. Some motherboards provide a B+M key slot that accepts either type, but the lane count may be limited.
Samsung NVMe SSDs use the M-key to use all four PCIe lanes. The same principle applies to other NVMe M.2 drives, so check the key of both the drive and the slot.
Lengths and common sizes
M.2 cards are identified by a four-digit code that gives width and length in millimeters. The first two digits are width and the last two are length. For example, 2280 means 22 mm wide and 80 mm long.
KIOXIA's client SSD product page lists M.2 2230, 2242, and 2280 as the available sizes for its EG, BG, and XG series, all single-sided.
PlayStation consoles accept M.2 drives in 2230, 2242, 2260, 2280, and 22110 sizes, with a Key M connector and PCIe Gen4x4 interface, as stated in the PlayStation M.2 SSD support page.
Checking compatibility
To choose an M.2 SSD, check three specifications: key type, interface, and length. The slot's key must match the drive's key, and the interface must be compatible, such as NVMe or SATA. The drive length must fit the mounting point.
Some slots support both SATA and NVMe, but others only one. For example, PlayStation consoles do not support M.2 SATA SSDs, only NVMe.
The same rules apply to laptops and desktops that use M.2. For users considering a gaming laptops system, the M.2 slot follows the same key and length standards. Always consult the motherboard or system manual for the exact slot type.
| Code | Width (mm) | Length (mm) |
|---|---|---|
| 2230 | 22 | 30 |
| 2242 | 22 | 42 |
| 2260 | 22 | 60 |
| 2280 | 22 | 80 |
| 22110 | 22 | 110 |
Frequently asked questions
What does the code M.2 2280 mean?
It indicates a width of 22 mm and a length of 80 mm. The first two digits are width and the last two are length.
What is the difference between B-key and M-key?
A B-key supports SATA or NVMe with up to 2 PCIe lanes, while an M-key supports NVMe with up to 4 PCIe lanes. An M-key slot is common for high-speed NVMe drives.
Can an M.2 SATA SSD fit in an NVMe slot?
It depends on the slot. Some slots support both, but others, such as those in PlayStation consoles, accept only NVMe. Check the slot specification.
How to determine the correct M.2 length for a device?
Measure the available space or consult the manual. The motherboard or system usually lists supported lengths like 2280 or 2230.
