A diskette is a random access, removable data storage medium that can be used with personal computers. The term usually refers to the magnetic medium housed in a rigid plastic cartridge measuring 3.5 inches square and about 2millimeters thick. Also called a "3.5-inch diskette," it can store up to 1.44 megabytes (MB) of data. Although many personal computers today come with a 3.5-inch diskette drive pre-installed, some notebook computers and centrally-administered desktop computers omit them.
Some older computers provide drives for magnetic diskettes that are 5.25 inches square, about 1 millimeter thick, and capable of holding 1.2 megabytes of data. These were sometimes called "floppy disks" or "floppies" because their housings are flexible. In recent years, 5.25-inch diskettes have been largely replaced by 3.5-inch diskettes, which are physically more rugged. Many people also call the newer hard-cased diskette a "floppy."
Magnetic diskettes are convenient for storing individual files and small programs. However, the magneto-optical (MO) disk is more popular for mass storage, backup, and archiving. An MO diskette is only a little larger, physically,than a conventional 3.5-inch magnetic diskette. But because of the sophisticated read/write technology, the MO diskette can store many times more data.