Editing Disk density

{{Short description|Storage density for magnetic disks}}{{Redir|Double density|the DOS disk compression software|Data Becker Double Density}}
{{More citations needed|date=May 2023}}
[[File:5.25"-Diskette.jpg|thumb|5¼-inch DD-Disk]]
'''Disk density''' is a capacity designation on [[magnetic storage]], usually [[floppy disk]]s. Each designation describes a set of characteristics that can affect the [[areal density (computer storage)|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 <span class="anchor" id="SD"></span><span class="anchor" id="DD"></span>==
''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, [[Differential Manchester encoding|FM encoding]], and a track width of {{convert|0.330|mm|abbr=on}} 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 <span class="anchor" id="QD"></span><span class="anchor" id="HD"></span>==
''SD'' (''1D'') and ''DD'' (''2D'') designations were generally identical to those of 8-inch disks.

''Quad density'' (QD or 4D<!-- BASF -->) doubles capacity over DD by narrowing the width of tracks to {{convert|0.160|mm|abbr=on}} for a density of 96&nbsp;tpi. Some manufacturers ([[Micropolis (company)|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 [[Commodore 8250|8250]] are rare instances of drives that used 375&nbsp;kbit/s GCR code instead of the usual 250&nbsp;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&nbsp;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 <span class="anchor" id="3.5-DD"></span><span class="anchor" id="3.5-HD"></span><span class="anchor" id="ED"></span><span class="anchor" id="TD"></span><span class="anchor" id="VHD"></span><span class="anchor" id="UHD"></span>==
''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 {{convert|0.115|mm|abbr=on}} for a density of 135&nbsp;tpi and 8,717&nbsp;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&nbsp;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]].<ref name="Mueller_1994_HW"/><ref name="Intel_1992_82077SL"/>

''Triple density'' (TD) triples the capacity over ED by tripling the track density and improving other parameters.<ref name="CW_1988_NEC"/><ref name="NEC_1991_uPD72070"/><ref name="NEC_PC88VA3"/> The drives used [[longitudinal recording]].<ref name="Intel_1992_82077SL"/>

== Overview ==
{| class="wikitable" style="text-align:center;"
|-
! Size
! colspan="2" | 8-inch
! colspan="4" | 5¼-inch
! colspan="5" | 3½-inch
|-
! Density
! SD
! DD
! SD
! DD
! QD
! HD
! colspan="2" | DD
! HD
! ED<ref name="Mueller_1994_HW"/>
! TD<ref name="NEC_1991_uPD72070"/>
|-
! Disk coating
| colspan="5" | Iron oxide<ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/>
| Cobalt<ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/>
| ?
| Iron oxide, Cobalt?<ref name="Mueller_1994_HW"/>
| Cobalt<ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/>
| Barium ferrite<ref name="Mueller_1994_HW"/>
| Barium ferrite [https://www.vogons.org/viewtopic.php?t=98550]
|-
! Coercivity <nowiki>[</nowiki>[[Oersted|Oe]]<nowiki>]</nowiki>
| colspan="5" | 290,<ref name="Johnson_2011_HDDD"/> 300<ref name="Scott_1990_UM"/><ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/> 
| 600,<ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/> 660,<ref name="Johnson_2011_HDDD"/> 670<ref name="Scott_1990_UM"/>
| ca. 600
| 600?,<ref name="Mueller_1994_HW"/><ref name="Yaskawa_1988_MR"/> 660,<ref name="Johnson_2011_HDDD"/> 670<ref name="Scott_1990_UM"/>
| 700,<ref name="Scott_1990_UM"/> 720<ref name="Johnson_2011_HDDD"/><ref name="Mueller_1994_HW"/>
| 750?,<ref name="Mueller_1994_HW"/> 1060,<ref name="Johnson_2011_HDDD"/> 1200
| ?
|-
! Coating thickness <nowiki>[</nowiki>[[μm]]<nowiki>]</nowiki>
| 110
| 110
| ?
| 100,<ref name="Scott_1990_UM"/> 2.5,<ref name="Johnson_2011_HDDD"/> 2.0-3.0<ref name="Yaskawa_1988_MR"/>
| ?
| 55,<ref name="Scott_1990_UM"/> 1.3,<ref name="Johnson_2011_HDDD"/> 1.0-1.5<ref name="Yaskawa_1988_MR"/>
| ?
| 65,<ref name="Scott_1990_UM"/> 1.9,<ref name="Johnson_2011_HDDD"/> 2.0-3.0<ref name="Yaskawa_1988_MR"/>
| 55,<ref name="Scott_1990_UM"/> 0.9,<ref name="Johnson_2011_HDDD"/> 1.0-1.5<ref name="Yaskawa_1988_MR"/>
| ?
| ?
|-
! [[Line code]]
| [[Digital FM|FM]]
| [[Modified Frequency Modulation|MFM]], [[M²FM]]<!-- Intel iSBC/ISIS only -->, FM/MFM<!-- DEC RX02 used a combination of FM and MFM --> or [[Group-coded recording|GCR]]
| FM
| colspan="2" | MFM or GCR
| MFM
| MFM<ref name="Epson_1984_PF-10"/>
| MFM or GCR<!-- Apple Macintosh -->
| colspan="3" | MFM
|-
! Track width [mm]
| colspan="4" | 0.330<ref name="Mueller_1994_HW"/>
| colspan="2" | 0.160<ref name="Mueller_1994_HW"/>
| ?
| colspan="3" | 0.115<ref name="Mueller_1994_HW"/>
| ?
|-
! Track density [tpi]
| colspan="4" | 48<ref name="Mueller_1994_HW"/>
| 96<ref name="Mueller_1994_HW"/> or 100
| 96<ref name="Mueller_1994_HW"/>
| 67.5<ref name="Epson_1984_PF-10"/>
| colspan="3" | 135<ref name="Mueller_1994_HW"/>
| 406.5<ref name="NEC_1991_uPD72070"/>
|-
! Bit density [bpi]
| colspan="5" | 5,876,<ref name="Intel_1992_82077SL"/><ref name="Mueller_1994_HW"/> 5,922<ref name="Williams_DSM"/>
| 9,646,<ref name="Mueller_1994_HW"/> 9,870<ref name="Intel_1992_82077SL"/>
| 8,650<ref name="Epson_1984_PF-10"/>
| 8,717<ref name="Intel_1992_82077SL"/><ref name="Mueller_1994_HW"/>
| 17,432,<ref name="Intel_1992_82077SL"/> 17,434<ref name="Mueller_1994_HW"/>
| 34,868<ref name="Intel_1992_82077SL"/><ref name="Mueller_1994_HW"/>
| 36,700<ref name="NEC_1991_uPD72070"/>
|-
! Recording direction
| colspan="9" | longitudinal&nbsp;/ horizontal<ref name="Mueller_1994_HW"/>
| perpendicular&nbsp;/ vertical<ref name="Mueller_1994_HW"/>
| longitudinal<ref name="Intel_1992_82077SL"/>&nbsp;/ horizontal<ref name="Mueller_1994_HW"/>
|}

== See also ==
*[[List of floppy disk formats]]

== References ==
{{reflist|refs=
<ref name="Scott_1990_UM">{{cite journal |title=More on Floppies |author-first=Greg |author-last=Scott |journal=U-M Computing News |publisher=[[University of Michigan]], Information Technology Division |date=1990-07-16 |volume=5 |number=12 |pages=10–11 |url=https://books.google.com/books?id=opXvAAAAMAAJ&pg=RA2-PA10 |access-date=2017-06-19 }}</ref>
<ref name="Epson_1984_PF-10">{{cite book |title=Epson PF-10 Operating Manual |publisher=[[Epson Corporation]] |location=Nagano, Japan |date=1984 |url=http://electrickery.xs4all.nl/comp/px8/doc/PF-10Manual.pdf |access-date=2017-06-19 |url-status=live |archive-url=https://web.archive.org/web/20170619024329/http://electrickery.xs4all.nl/comp/px8/doc/PF-10Manual.pdf |archive-date=2017-06-19}} (NB. The [[Epson PF-10]] is an external diskette drive for the [[Epson PX-8]] (Geneva) CP/M laptop.)</ref>
<ref name="NEC_1991_uPD72070">{{cite book |title=NEC μPD72070 - Floppy Disk Controller Specification Version 2.0 |version=2.0 preliminary |publisher=[[NEC Corporation]] |date=October 1991 |url=http://dec8.info/Apple/uPD72070.pdf |access-date=2017-03-20 |url-status=live |archive-url=https://web.archive.org/web/20170320235834/http://dec8.info/Apple/uPD72070.pdf |archive-date=2017-03-20}}</ref>
<ref name="CW_1988_NEC">{{cite journal |title=Hitachi-Maxell bietet NEC neue 12,5-MB-Floppy an |date=1988-07-29 |location=Tokio, Japan |author=IDG |author-link=IDG |journal=[[Computerwoche]] |language=German |url=https://www.computerwoche.de/a/hitachi-maxell-bietet-nec-neue-12-5-mb-floppy-an,1155888 |access-date=2017-06-19 |url-status=live |archive-url=https://web.archive.org/web/20170619203621/https://www.computerwoche.de/a/hitachi-maxell-bietet-nec-neue-12-5-mb-floppy-an,1155888 |archive-date=2017-06-19 |quote=[…] [[Hitachi-Maxell]] hat ein 3½-Zoll-Diskettenlaufwerk mit einer Speicherkapazität von 12.5&nbsp;MB entwickelt. Nach eigenen Angaben will das Unternehmen auf [[OEM]]-Basis den Hersteller [[NEC]] mit den Geräten versorgen. Dort sollen sie als externer Speicher für die neue PC-Serie [[PC88VA3]] eingesetzt werden. Die Laufwerke mit der Bezeichnung PC&nbsp;FD810.1 sind voraussichtlich ab dem vierten Quartal dieses Jahres lieferbar. Bis Ende 1989 will NEC die ersten {{val|150000}} Geräte verkauft haben. […]}}</ref>
<ref name="NEC_PC88VA3">{{cite web |title=PC-88VA <ハードウエア> |language=Japanese |date=1995-06-24 |url=http://www.pc88.gr.jp/va/va-hard.html |access-date=2017-06-18 |url-status=live |archive-url=https://web.archive.org/web/20170618120229/http://www.pc88.gr.jp/va/va-hard.html |archive-date=2017-06-18}}</ref>
<ref name="Intel_1992_82077SL">{{cite book |title=Intel 82077SL for Super-Dense Floppies |author-first=Katen A. |author-last=Shah |publisher=[[Intel Corporation]], IMD Marketing |orig-year=September 1992, April 1992 |edition=2 |date=1996 |id=AP-358, 292093-002 |type=Application Note |url=http://www.pix.net/languard/pdfs/29209302.pdf |access-date=2017-06-19 |url-status=live |archive-url=https://web.archive.org/web/20170619210818/http://www.pix.net/languard/pdfs/29209302.pdf |archive-date=2017-06-19}}</ref>
<ref name="Johnson_2011_HDDD">{{cite web |date=2011-08-12 |orig-year=July 2009 |title=Use of HD and DD drives, diskettes |editor-first=Herbert R.<!-- Herb --> |editor-last=Johnson |author-first=Charles P.<!-- Chuck --> |author-last=Guzis |url=http://www.retrotechnology.com/herbs_stuff/guzis.html |access-date=2017-06-19 |url-status=live |archive-url=https://web.archive.org/web/20170619213807/http://www.retrotechnology.com/herbs_stuff/guzis.html |archive-date=2017-06-19}} (NB. Based on specifications by the National Media Laboratory, associated with [[3M]]/[[Imation]].)</ref>
<ref name="Mueller_1994_HW">{{cite book |title=Hardware-Praxis - PCs warten reparieren, aufrüsten und konfigurieren |author-first=Scott |author-last=Mueller |date=1994 |isbn=3-89319-705-2 |edition=3rd |publisher=[[Addison-Wesley Publishing Company]] |language=German}}</ref>
<ref name="Yaskawa_1988_MR">{{cite book |title=Magnetic Recording |chapter=3. Data Storage on Flexible Disks |author-last1=Yaskawa |author-first1=Seiichi |author-last2=Heath |author-first2=John |editor-last1=Mee |editor-first1=C. Denis |editor-last2=Daniel |editor-first2=Eric D. |publisher=[[McGraw-Hill Book Company]] |date=1988 |volume=II: Computer Data Storage |edition=1st |isbn=0-07-041272-3 |pages=130–169}}</ref>
<ref name="Williams_DSM">{{cite book |title=Disk Service Manual III - Unleash the Power of Your System! |chapter=FM vs. MFM encoding |author-first=John J. |author-last=Williams |publisher=Consumertronics Co. |edition=III |location=Alamogordo, New Mexico, USA |url=http://oldcomputers.dyndns.org/public/pub/manuals/disk_service_manual_iii.pdf |access-date=2021-11-02 }}</ref>
}}

== External links ==
* {{cite web |url=http://www.hardware-bastelkiste.de/floppy.html |title=Floppy-Disketten-Laufwerke |trans-title=Floppy disk drives |access-date=2017-06-19 |author=(M)Tronics SCS |language=German |date=2007-05-20 |url-status=dead |archive-url=https://web.archive.org/web/20170619194609/http://www.hardware-bastelkiste.de/index.html?floppy.html |archive-date=2017-06-19 }}

[[Category:Floppy disk computer storage]]