(Or "floppy", "diskette") A small, portable plastic disk coated in a magnetisable substance used for storing computer data, readable by a computer with a floppy disk drive. The physical size of disks has shrunk from the early 8 inch, to 5 1/4 inch ("minifloppy") to 3 1/2 inch ("microfloppy") while the data capacity has risen.

These disks are known as "floppy" disks (or diskettes) because the disk is flexible and the read/write head is in physical contact with the surface of the disk in contrast to "hard disks" (or winchesters) which are rigid and rely on a small fixed gap between the disk surface and the heads. Floppies may be either single-sided or double-sided.

3.5 inch floppies are less floppy than the larger disks because they come in a stiff plastic "envelope" or case, hence the alternative names "stiffy" or "crunchy" sometimes used to distinguish them from the floppier kind.

The following formats are used on IBM PCs and elsewhere:

 Capacity  Density  Width
  360K           double   5.25"
  720K           double   3.5"
  1.2M           high            5.25"
 1.44M           high            3.5"

Double denisty and high density are usually abbreviated DD and HD. HD 3.5 inch disks have a second hole in the envelope and an overlapping "HD" logo.