M.2 – A small gumstick card-sized format used for flash memory drives. It can be single or double-sided and has a fixed size. The cards are described by 4- or 5-digit numbers which indicate their size. An M.2 2280 card is 22mm wide by 80mm long. The card widths and lengths can vary. M.2 cards fit into SATA or PCIe slots.