Disk density is a capacity designation on magnetic storage, usually

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...

s. Each designation describes a set of characteristics that can affect the areal density of a disk or the efficiency of the encoded data. Such characteristics include

modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

method, track width, coercivity, and magnetic field direction.

8-inch media

''Single density'' (SD or 1D) describes the first generation of floppy disks that use an iron oxide coating. Floppy drives utilize 300-oersted write heads, FM encoding, and a track width of for a density of 48 tracks-per-inch (tpi) and 5,876 bits-per-inch (bpi). ''Double density'' (DD or 2D) doubles capacity over SD by replacing FM encoding with an improved line code, such as modified frequency modulation (MFM), modified modified frequency modulation (M²FM), FM/MFM or group coded recording (GCR).

5¼-inch media

''SD'' (''1D'') and ''DD'' (''2D'') designations were generally identical to those of 8-inch disks. ''Quad density'' (QD or 4D) doubles capacity over DD by narrowing the width of tracks to for a density of 96 tpi. Some manufacturers ( Micropolis, Tandon, Micro Peripherals (MPI),

Teac () is a Japanese electronics manufacturer. TEAC was created by the merger of the Tokyo Television Acoustic Company, founded in 1953, and the Tokyo Electro-Acoustic Company, founded in 1956. Overview TEAC has four divisions: *TASCAM - con ...

) used a track density of 100 tpi for quad-density drives, which were incompatible with 96 tpi models. The Commodore 8050 and 8250 are rare instances of drives that used 375 kbit/s GCR code instead of the usual 250 kbit/s double-density format and they could store roughly 500 kilobytes on one side of a disk. ''High density'' (HD) improves capacity by utilizing a 96 tpi track density in conjunction with improved cobalt disk coating and stronger 600-oersted write heads, allowing 9,646 bpi to be written.

3½-inch media

''Double density'' (DD) 3½-inch disks use an iron oxide coating, just as with 5¼-inch DD/QD disks. However, drives utilize stronger 670-oersted write heads and a narrower track width of for a density of 135 tpi and 8,717 bpi. ''High density'' (HD) 3½-inch disks switch to a cobalt disk coating, just as with 5¼-inch HD disks. Drives use 700-oersted write heads for a density of 17,434 bpi. ''Extra-high density'' (ED) doubles the capacity over HD by using a barium ferrite coating and a special write head that allows the use of perpendicular recording. ''Triple density'' (TD) triples the capacity over ED by tripling the track density and improving other parameters. The drives used longitudinal recording.

Overview

References

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