A designation of floppy disks that have twice the storage capacity of a Single Density floppy (both of which are pretty much obsolete nowadays). Double density 5¼-inch disks for PCs can hold 360 kB of data while double density 3½-inch disks can store a whopping 720 kB. More efficient systems like the Amiga (and some PC utilities like fdformat) can format DD floppies to 880 kB capacity.