(1) (MB) (MegaByte) One million bytes (1,000,000 bytes or 1,048,576 bytes). See mega and space/time.

(2) (MB) (MotherBoard) On references to basic hardware components, MB often means motherboard or mainboard.

(3) (Mb) (MegaBit) One million bits (1,000,000 bits or 1,048,576 bits). In communications, mega typically refers to 1,000,000. In storage, mega typically refers to 1,048,576. Lower case "b" for bit and "B" for byte are not always followed and often misprinted. Thus, Mb may refer to megabyte. See mega and space/time.