Double density

Double Density usually refers to a physical format in a magnetic storage system that uses twice as many bits per length unit as the basic format.

In 3.5" Floppy disks double density marks a disk format that uses 9 sectors of 512 bytes per track, For a total capacity of 720kB in a two-sided 80 track floppy disk.

Curently (2003) used 3.5" floppy disks are high density[?], which doubles the capacity and bit density of double density.

The term double density can also be applied to magnetic tapes.