A floppy disk is a data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. Floppy disks are read and written by a floppy disk drive or FDD, the initials of which should not be confused with "fixed disk drive," which is another term for a (nonremovable type of) hard disk drive. Invented by IBM, floppy disks in 8-inch (200 mm), 5¼-inch (133⅓ mm), and 3½-inch (90 mm) formats enjoyed many years as a popular and ubiquitous form of data storage and exchange, from the mid-1970s to the late 1990s. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have now been largely superseded by USB flash drives, External Hard Drives, CD-ROMs, DVD-ROMs, an