Disk density

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File:5.25"-Diskette.jpg
5¼-inch DD-Disk

Disk density is a capacity designation on magnetic storage, usually floppy disks. 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 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 Template:Convert 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 Template:Convert for a density of 96 tpi. Some manufacturers (Micropolis, Tandon, Micro Peripherals (MPI), Teac) 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 Template:Convert 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.[1][2]

Triple density (TD) triples the capacity over ED by tripling the track density and improving other parameters.[3][4][5] The drives used longitudinal recording.[2]

Overview

Size 8-inch 5¼-inch 3½-inch
Density SD DD SD DD QD HD DD HD ED[1] TD[4]
Disk coating Iron oxide[1][6] Cobalt[1][6] ? Iron oxide, Cobalt?[1] Cobalt[1][6] Barium ferrite[1] Barium ferrite [1]
Coercivity [Oe] 290,[7] 300[8][1][6] 600,[1][6] 660,[7] 670[8] ca. 600 600?,[1][6] 660,[7] 670[8] 700,[8] 720[7][1] 750?,[1] 1060,[7] 1200 ?
Coating thickness [μm] 110 110 ? 100,[8] 2.5,[7] 2.0-3.0[6] ? 55,[8] 1.3,[7] 1.0-1.5[6] ? 65,[8] 1.9,[7] 2.0-3.0[6] 55,[8] 0.9,[7] 1.0-1.5[6] ? ?
Line code FM MFM, M²FM, FM/MFM or GCR FM MFM or GCR MFM MFM[9] MFM or GCR MFM
Track width [mm] 0.330[1] 0.160[1] ? 0.115[1] ?
Track density [tpi] 48[1] 96[1] or 100 96[1] 67.5[9] 135[1] 406.5[4]
Bit density [bpi] 5,876,[2][1] 5,922[10] 9,646,[1] 9,870[2] 8,650[9] 8,717[2][1] 17,432,[2] 17,434[1] 34,868[2][1] 36,700[4]
Recording direction longitudinal / horizontal[1] perpendicular / vertical[1] longitudinal[2] / horizontal[1]

See also

References

Template:Reflist

External links

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  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa Cite error: Invalid <ref> tag; no text was provided for refs named Mueller_1994_HW
  2. ↑ a b c d e f g h Cite error: Invalid <ref> tag; no text was provided for refs named Intel_1992_82077SL
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named CW_1988_NEC
  4. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named NEC_1991_uPD72070
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named NEC_PC88VA3
  6. ↑ a b c d e f g h i j Cite error: Invalid <ref> tag; no text was provided for refs named Yaskawa_1988_MR
  7. ↑ a b c d e f g h i Cite error: Invalid <ref> tag; no text was provided for refs named Johnson_2011_HDDD
  8. ↑ a b c d e f g h Cite error: Invalid <ref> tag; no text was provided for refs named Scott_1990_UM
  9. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Epson_1984_PF-10
  10. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Williams_DSM
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