M.2

M.2's size code follows a simple pattern -- the first two digits are width in millimeters, the rest is length, so 2280 reads as 22mm wide by 80mm long. 2280 is the most common size in desktops and laptops; shorter 2242 and 2230 modules show up in smaller ultrabooks and handhelds, and 22110 (110mm) is mostly reserved for high-capacity enterprise drives that need the extra board space.

The key notch position matters as much as the physical size. B-key (pins 12-19) supports SATA or PCIe x2; M-key (pins 59-66) supports SATA or the full PCIe x4 lane count NVMe drives need for their top speeds. A module cut with both notches (B+M key) is commonly assumed to get the best of both, but it's actually capped at whatever the narrower B-key side supports -- SATA or PCIe x2 -- not the full x4 NVMe bandwidth. M.2 was introduced by PCI-SIG and SATA-IO in November 2013 under the working name NGFF (Next Generation Form Factor), replacing both mSATA and Mini PCIe.