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.
Currently (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.
Density of all matter depends on temperature; the density of a mixture may depend on its composition, and the density of a gas on its pressure.
The specific gravity of a material is defined as the ratio of its density to the density of some standard material, such as water at a specified temperature, for example, 60°F (15.6°C), or, for gases the basis may be air at standard temperature and pressure.
Density of wood is influenced by rate of growth, percentage of late wood and in individual pieces, the proportion of the heartwood.
Doubledensity 3.5 inch diskette drives were available on some PC clones, and then first used by IBM on the IBM PC Convertible in 1984 or 1985.
The doubledensity 3.5 inch diskette was successful; the diskettes held more than the original doubledensity 5.25 inch diskettes, the media was protected better, and they were convenient to use.
Doubledensity media: this is the older type of media that was common in the early to mid 1980s.
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