M.2 SSD form factor
M.2 SSDs are rectangular. They are 22 millimeters (mm) wide and usually 60 mm or 80 mm long, although there are also 30 mm, 42 mm and 110 mm length cards. Longer length M.2 drives usually hold more NANDchips for extra capacity than the shorter versions. M.2 drives can be single or double-sided. The card size is identified by a four- or five-digit number. The first two digits are the width and the remaining numbers are the length. For example, a 2260 card is 22 mm wide and 60 mm long.
The 22 mm width is standard for desktop and laptops. An 80 mm or 110 mm length card can hold 8 NAND chips for 1 TB of capacity.
M.2 module keys
Keys, notches in the edge connectors of M.2 modules, distinguish the types of M.2 products.
M.2 SSD modules plug into circuit boards through mating connectors on either side. Unlike mSATA, M.2 SSD cards have two types of connectors, also known as sockets: B key sockets and M key sockets. A single card can also have B and M keys. The type of key determines the number of PCIe lanes the socket supports. A B key holds one or two PCIe lanes, while an M key holds up to four PCIe lanes. The B key edge connector is six pins wide and the M key edge connector is five pins wide.
For Wi-Fi and Bluetooth wireless adapters, M.2 cards are keyed for A and E slots in a motherboard. Most M.2 wireless cards support both A and E key slots.
