Editing Floppy disk (section)

==Sizes==
{{Main|Floppy disk format|List of floppy disk formats}}
While the original IBM 8-inch disk was actually so defined, the other sizes are defined in the metric system, their usual names being but rough approximations.{{Refn | {{Citation | title = X3.162 | date = 1994 | publisher = ANSI | url = https://webstore.ansi.org/Standards/INCITS/ANSIX31621988R1994 | quote = Information Systems – Unformatted Flexible Disk Cartridge for Information Interchange, 5.25 in (130 mm), 96 Tracks per inch (3.8 Tracks per Millimeter), General, Physical, and Magnetic Requirements (includes ANSI X3.162/TC-1-1995) Specifies the general, physical, and magnetic requirements for interchangeability for the two-sided, 5.25 in (130 mm) flexible disk cartridge | access-date = 28 February 2022 | archive-date = 28 February 2022 | archive-url = https://web.archive.org/web/20220228185002/https://webstore.ansi.org/Standards/INCITS/ANSIX31621988R1994 | url-status = dead }}}}

Different sizes of floppy disks are mechanically incompatible, and disks can fit only one size of drive. Drive assemblies with both 3½-inch and 5¼-inch slots were available during the transition period between the sizes, but they contained two separate drive mechanisms. In addition, there are many subtle, usually software-driven incompatibilities between the two. 5¼-inch disks formatted for use with Apple II computers would be unreadable and treated as unformatted on a Commodore. As [[computer platforms]] began to form, attempts were made at interchangeability. For example, the "[[SuperDrive]]" included from the [[Macintosh SE]] to the [[Power Macintosh G3]] could read, write and format IBM PC format 3½-inch disks, but few IBM-compatible computers had drives that did the reverse. 8-inch, 5¼-inch and 3½-inch drives were manufactured in a variety of sizes, most to fit standardized [[drive bay]]s. Alongside the common disk sizes were [[floppy disk variants|non-classical sizes]] for specialized systems.{{fact|date=June 2024}}

==={{anchor|8.0}}8-inch floppy disk===
[[File:8-inch floppy disk - IZOT, Bulgaria.jpg|thumb|upright|8-inch floppy disk]]
Floppy disks of the first standard are 8 inches in diameter,<ref name= "Teja_1985">{{cite book |title= The Designer's Guide to Disk Drives |first=Edward R. |last=Teja |publisher=[[Reston Publishing Company, Inc.|Reston]] / [[Prentice-Hall Company|Prentice hall]] |location=Reston, Virginia, US |edition=1st |date=1985 |isbn= 0-8359-1268-X}}</ref> protected by a flexible plastic jacket. It was a read-only device used by IBM as a way of loading [[microcode]].<ref>{{cite web |title=Floppy Disk |url= http://grok.lsu.edu/Article.aspx?articleid=11150 |publisher=[[Louisiana State University]] |access-date= 2013-12-02 |archive-url= https://web.archive.org/web/20141018004741/http://grok.lsu.edu/Article.aspx?articleid=11150 |archive-date= 2014-10-18 |url-status=dead}}</ref> Read/write floppy disks and their drives became available in 1972, but it was IBM's 1973 introduction of the [[IBM 3740|3740 data entry system]]<ref>{{cite web|url= http://www-03.ibm.com/ibm/history/exhibits/rochester/rochester_4016.html| publisher = IBM | title = 3740 |date=23 January 2003|website= Archives |access-date= 13 October 2014|url-status= dead |archive-url=https://web.archive.org/web/20171225162318/http://www-03.ibm.com/ibm/history/exhibits/rochester/rochester_4016.html|archive-date=25 December 2017}}</ref> that began the establishment of floppy disks, called by IBM the ''Diskette 1'', as an industry standard for information interchange. Diskettes formatted for this system stored 242,944 bytes.<ref>{{Cite book|year= 1974 | via = Stuttgart University |url= http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/3740/GA21-9152-2_IBM_3740_DataEntrySystem_SystemSummary_and_InstallationManual_PhysicalPlanning_Jun74.pdf |title=IBM 3740 Data Entry System System Summary and Installation Manual – Physical Planning|publisher=IBM|page = 2 |quote=The diskette is about 8" (20 cm) square and has a net capacity of 1898 128-character records – about one day's data entry activity. Each of the diskette's 73 magnetic recording tracks available for data entry can hold 26 sectors of up to 128 characters each.|access-date= 2019-03-07|archive-url=https://web.archive.org/web/20170215173042/http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/3740/GA21-9152-2_IBM_3740_DataEntrySystem_SystemSummary_and_InstallationManual_PhysicalPlanning_Jun74.pdf |archive-date=2017-02-15 |url-status=live}}</ref> Early [[microcomputer]]s used for engineering, business, or word processing often used one or more 8-inch disk drives for removable storage; the [[CP/M]] operating system was developed for microcomputers with 8-inch drives.<ref name="Kildall_1980_CPM">{{cite magazine |title=The History of CP/M, The Evolution Of An Industry: One Person's Viewpoint |author-first=Gary Arlen |author-last=Kildall |author-link=Gary Arlen Kildall |date=January 1980 |magazine=[[Dr. Dobb's Journal]] |pages=6–7 |volume=5 |issue=1 <!-- |number=-->#41 |url=http://www.retrotechnology.com/dri/CPM_history_kildall.txt |access-date=2013-06-03 |url-status=live |archive-url=https://web.archive.org/web/20161124221907/http://www.retrotechnology.com/dri/CPM_history_kildall.txt |archive-date=2016-11-24}}</ref>

The family of 8-inch disks and drives increased over time and later versions could store up to 1.2&nbsp;MB;<ref>{{cite web |url=http://www.cpm.z80.de/manuals/IBM_GA21_9182_4.txt |title=The IBM Diskette General Information Manual | place = [[Germany|DE]] |access-date= 2014-10-13 | publisher = Z80 |archive-url= https://web.archive.org/web/20141028015720/http://www.cpm.z80.de/manuals/IBM_GA21_9182_4.txt|archive-date=2014-10-28 |url-status=live}}</ref> many microcomputer applications did not need that much capacity on one disk, so a smaller size disk with lower-cost media and drives was feasible. The 5¼-inch drive succeeded the 8-inch size in many applications, and developed to about the same storage capacity as the original 8-inch size, using higher-density media and recording techniques.{{fact|date=June 2024}}

==={{anchor|5.25|5.25-inch floppy disk|5¼-inch floppy disk}}5¼-inch floppy disk===
{{multiple image
| total_width = 400
| image1      = 5.25 inch floppy disk, front and back.jpg
| caption1     = 5¼-inch floppies, front and back
| image2       = 5.25 in. floppy disk drive top.jpg
| caption2     = Uncovered 5¼‑inch disk mechanism with disk inserted
}}
The head gap of an 80‑track high-density (1.2&nbsp;MB in the [[Modified Frequency Modulation|MFM]] format) 5¼‑inch drive (a.k.a. '''Mini diskette''', '''Mini disk''', or [[Shugart Associates|Minifloppy]]) is smaller than that of a 40‑track double-density (360&nbsp;KB if double-sided) drive but can also format, read and write 40‑track disks provided the controller supports double stepping or has a switch to do so. 5¼-inch 80-track drives were also called '''hyper drives'''.<ref group="nb" name="NB_Hyperdrive"/> A blank 40‑track disk formatted and written on an 80‑track drive can be taken to its native drive without problems, and a disk formatted on a 40‑track drive can be used on an 80‑track drive. Disks written on a 40‑track drive and then updated on an 80 track drive become unreadable on any 40‑track drives due to track width incompatibility.{{fact|date=June 2024}}

Single-sided disks were coated on both sides, despite the availability of more expensive double sided disks. The reason usually given for the higher price was that double sided disks were certified error-free on both sides of the media. Double-sided disks could be used in some drives for single-sided disks, as long as an index signal was not needed. This was done one side at a time, by turning them over ([[flippy disk]]s); more expensive dual-head drives which could read both sides without turning over were later produced, and eventually became used universally.{{fact|date=June 2024}}

==={{anchor|3.5|3.5-inch floppy disk|3½-inch floppy disk|microfloppy}}3½-inch floppy disk===
[[File:Floppy disk internal diagram 8.svg|thumb|upright|Internal parts of a 3½-inch floppy disk.
{{ordered list
| list_style=margin-left:0;
| item_style=margin-bottom:0; list-style-position:inside;
| A hole that indicates a high-capacity disk.
| The hub that engages with the drive motor.
| A shutter that protects the surface when removed from the drive.
| The plastic housing.
| A polyester sheet reducing friction against the disk media as it rotates within the housing.
| The magnetic coated plastic disk.
| A schematic representation of one sector of data on the disk; the tracks and sectors are not visible on actual disks.
| The [[write protection]] tab.
}}]]

[[File:Floppy Disk Drive SDF-321B.jpg|thumb|left|A 3½-inch floppy disk drive]]

In the early 1980s, many manufacturers introduced smaller floppy drives and media in various formats.<ref name="microcomputing198308_barbier">{{ cite magazine | url=https://archive.org/details/kilobaudmagazine-1983-08/page/n53/mode/2up | title=Pocket Size Floppies: Revolution or Rip-Off? | magazine=Microcomputing | last1=Barbier | first1=Ken | date=August 1983 | access-date=12 December 2024 | pages=52–54 }}</ref>  A consortium of 21 companies eventually settled on a 3½-inch design known as the ''Micro diskette'', ''Micro disk'', or ''Micro floppy'', similar to a [[Sony]] design but improved to support both single-sided and double-sided media, with formatted capacities generally of 360&nbsp;KB and 720&nbsp;KB respectively. Single-sided drives of the consortium design first shipped in 1983,<ref>{{cite news |last=Shea |first=Tom |date=1983-06-13 |url=https://books.google.com/books?id=zS8EAAAAMBAJ&pg=PA8 |title=Shrinking drives increase storage |work=[[InfoWorld]] |pages=1, 7, 8, 9, 11 |quote=Shugart is one of the major subscribers to the 3{{citefrac|1|2}}-inch micro-floppy standard, along with Sony and 20 other company&nbsp;... Its single-sided SA300 micro-floppy drive offers 500K of unformatted storage. Shugart's Kevin Burr said the obvious next step is to put another 500K of storage on the other side of the diskette and that the firm will come out with a double-sided 1-megabyte micro-floppy drive soon.}}</ref> and double-sided in 1984. The double-sided, high-density 1.44&nbsp;MB (actually 1440&nbsp;KiB = 1.41&nbsp;MiB or 1.47 MB) disk drive, which would become the most popular, first shipped in 1986.<ref>{{cite book |date=November 1986 |title=1986 Disk/Trend Report – Flexible Disk Drives |publisher=Disk/Trend, Inc. |page=FSPEC-59}} Reports Sony shipped in 1Q 1986</ref> The first [[Macintosh 128K|Macintosh]] computers used single-sided 3½-inch floppy disks, but with 400&nbsp;KB formatted capacity. These were followed in 1986 by double-sided 800&nbsp;KB floppies. The higher capacity was achieved at the same recording density by varying the disk-rotation speed with head position so that the linear speed of the disk was closer to constant. Later Macs could also read and write 1.44&nbsp;MB HD disks in PC format with fixed rotation speed. Higher capacities were similarly achieved by Acorn's [[RISC OS]] (800&nbsp;KB for DD, 1,600&nbsp;KB for HD) and [[AmigaOS]] (880&nbsp;KB for DD, 1,760&nbsp;KB for HD).<!-- Apparently Amiga used ''low'' density floppies spun at half the speed that IBM compatibles used? -->

All 3½-inch disks have a rectangular hole in one corner which, if obstructed, write-enables the disk. A sliding detented piece can be moved to block or reveal the part of the rectangular hole that is sensed by the drive. The HD 1.44&nbsp;MB disks have a second, unobstructed hole in the opposite corner that identifies them as being of that capacity.{{fact|date=June 2024}}

In IBM-compatible PCs, the three densities of 3½-inch floppy disks are backwards-compatible; higher-density drives can read, write and format lower-density media. It is also possible to format a disk at a lower density than that for which it was intended, but only if the disk is first thoroughly demagnetized with a bulk eraser, as the high-density format is magnetically stronger and will prevent the disk from working in lower-density modes.{{fact|date=June 2024}}

Writing at different densities than those at which disks were intended, sometimes by altering or drilling holes, was possible but not supported by manufacturers. A hole on one side of a 3½-inch disk can be altered as to make some [[disk drives]] and [[operating system]]s treat the disk as one of higher or lower density, for bidirectional compatibility or economical reasons.{{clarify|date=March 2013}}<ref>{{cite web |title=Managing Disks |url=http://www.carolrpt.com/disks.htm |access-date=2006-05-25 |archive-url=https://web.archive.org/web/20060524021845/http://www.carolrpt.com/disks.htm |archive-date=2006-05-24 |url-status=live}}</ref><ref>{{cite news |title=A question of floppies | newspaper=Jla Forums |url=http://www.jlaforums.com/viewtopic.php?p=22991294 |access-date=2011-02-20 |archive-url=https://web.archive.org/web/20111001231411/http://www.jlaforums.com/viewtopic.php?p=22991294 |archive-date=2011-10-01 |url-status=live}}</ref> Some computers, such as the [[PS/2]] and [[Acorn Archimedes]], ignored these holes altogether.<ref>{{cite web |title=Formatting 720K Disks on a 1.44MB Floppy |work=Floppy Drive |url=http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB |access-date=2011-02-11 |archive-url=https://web.archive.org/web/20110723160004/http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB |archive-date=2011-07-23 |url-status=live}}</ref>

===Other sizes===
{{Main|Floppy disk variants}}
Other smaller floppy sizes were proposed, especially for portable or pocket-sized devices that needed a smaller storage device.
* [[Tabor Drivette|3¼-inch floppies]] otherwise similar to 5¼-inch floppies were proposed by [[Tabor Corporation|Tabor]] and [[Dysan]].
* Three-inch disks similar in construction to 3½-inch were manufactured and used for a time, particularly by [[Amstrad#Computer product lines|Amstrad]] computers and word processors.
* A two-inch nominal size known as the [[Video Floppy]] was introduced by Sony for use with its Mavica still video camera.<ref>{{cite web|title=Sony / Canon 2 Inch Video Floppy|url=http://www.obsoletemedia.org/2-inch-floppy-disk-video-floppy/|website=Museum of Obsolete Media|access-date=4 January 2018|date=2013-05-02|archive-url=https://web.archive.org/web/20180113005125/http://www.obsoletemedia.org/2-inch-floppy-disk-video-floppy/|archive-date=13 January 2018|url-status=live}}</ref>
* An incompatible two-inch floppy produced by Fujifilm called the LT-1 was used in the [[Zenith Minisport]] portable computer.<ref>{{cite web|title=2 inch lt1 floppy disk|url=http://www.obsoletemedia.org/lt-1/|website=Museum of Obsolete Media|access-date=4 January 2018|date=2017-07-22|archive-url=https://web.archive.org/web/20180104221008/http://www.obsoletemedia.org/lt-1/|archive-date=4 January 2018|url-status=live}}</ref>
None of these sizes achieved much market success.<ref>Disk/Trend Report-Flexible Disk Drives, Disk/Trend Inc., November 1991, pp. SUM-27</ref>

===Sizes, performance and capacity===
Floppy disk size is often referred to in inches, even in countries using [[SI|metric]] and though the size is defined in metric. The ANSI specification of 3½-inch disks is entitled in part "90 mm (3.5-inch)" though 90&nbsp;mm is closer to 3.54&nbsp;inches.<ref>ANSI X3.137, One- and Two-Sided, Unformatted, 90-mm (3.5-inch) 5,3-tpmm (135-tpi), Flexible Disk Cartridge for 7958 bpr Use. General, Physical and Magnetic Requirements.</ref> Formatted capacities are generally set in terms of [[kilobyte]]s and [[megabyte]]s.
<!--Please be careful when changing prefixes; k = 1000 and K = 1024 and note that M may mean either 1,000,000 or 1,048,576 or something else depending upon context -->
{|class="wikitable"
|+ Historical sequence of floppy disk formats
<br/>In quantities of bits (b) or bytes (B)<br>Prefixes: k = 1,000; K = 1,024; M may mean 1,000,000 or 1,048, 576 or some other multiple.
|-
! Disk format
! Year introduced
! Formatted storage capacity
! Marketed capacity
|-
| style="text-align: left" | 8-inch: IBM 23FD (read-only)
| style="text-align: center" | 1971
| 81.664 kB<ref name="research.ibm.com">{{Cite journal
| last       = Engh
| first      = James T.
| date       = September 1981
| title      = The IBM Diskette and Diskette Drive
| journal    = IBM Journal of Research and Development
| volume = 25
| issue = 5
| pages      = 701–710| doi = 10.1147/rd.255.0701
}}</ref>
| Not marketed commercially
|-
| style="text-align: left" | 8-inch: Memorex 650
| style="text-align: center" | 1972
| 175 kB<ref name="memorex650">{{cite web|title=Memorex 650 Flexible Disc File|url=http://corphist.computerhistory.org/corphist/documents/doc-4407890383ae1.pdf|url-status=dead|archive-url=https://web.archive.org/web/20110725192620/http://corphist.computerhistory.org/corphist/documents/doc-4407890383ae1.pdf|archive-date=2011-07-25|access-date=2011-06-22}}</ref>
| 1.5 megabit full track<ref name="memorex650" />
|-
| style="text-align: left" | 8-inch: SS SD<br>IBM 33FD / Shugart 901
| style="text-align: center" | 1973
| 242.844 kB<ref name="research.ibm.com"/>
| 3.1 megabit unformatted
|-
| style="text-align: left" | 8-inch: DS SD<br>IBM 43FD / Shugart 850
| style="text-align: center" | 1976
| 568.320 kB<ref name="research.ibm.com"/>
| 6.2 megabit unformatted
|-
| style="text-align: left" | 5¼-inch (35 track) Shugart SA 400
| style="text-align: center" | 1976<ref>{{cite journal |last=Sollman |first=George |date=July 1978 |title=Evolution of the Minifloppy Product Family |journal=IEEE Transactions on Magnetics |volume=14 |issue=4 |pages=160–66 |doi=10.1109/TMAG.1978.1059748 |bibcode=1978ITM....14..160S |s2cid=32505773 |issn=0018-9464}}</ref>
| 87.5 KB<ref>{{cite web|date=2007-06-25|title=Shugart SA 400 Datasheet|url=http://www.swtpc.com/mholley/SA400/SA400_Index.htm|url-status=dead|archive-url=https://web.archive.org/web/20140527094602/http://www.swtpc.com/mholley/SA400/SA400_Index.htm|archive-date=2014-05-27|access-date=2011-06-22|publisher=Swtpc}}</ref>
| 110 kB
|-
| style="text-align: left" | 8-inch DS DD<br>[[List of floppy disk formats#IBM 8-inch formats|IBM 53FD]] / Shugart 850
| style="text-align: center" | 1977
| 962–1,184&nbsp;KB depending upon sector size
| 1.2&nbsp;MB
|-
| style="text-align: left" | 5¼-inch DD
| style="text-align: center" | 1978
| 360 or 800&nbsp;KB
| 360 KB
|-
| style="text-align: left" | 5¼-inch Apple Disk II (Pre-DOS 3.3)
| style="text-align: center" | 1978
| 113.75 KB (256 byte sectors, 13 sectors/track, 35 tracks)
| 113 KB
|-
| style="text-align: left" | 5¼-inch Atari DOS 2.0S
| style="text-align: center" | 1979
| 90 KB (128 byte sectors, 18 sectors/track, 40 tracks)
| 90 KB
|-
| style="text-align: left" | 5¼-inch [[Commodore DOS]] 1.0 (SSDD)
| style="text-align: center" | 1979<ref>{{cite magazine|title=New Commodore Products: A Quick Review|last=Beals|first=Gene|magazine=PET User Notes|location=Montgomeryville, Pennsylvania|volume=2|issue=1|date=n.d.|page=2|url=http://archive.6502.org/publications/pet_user_notes/pet_user_notes_v2_i1_may_1979.pdf|access-date=2018-10-07|archive-url=https://web.archive.org/web/20160611084859/http://archive.6502.org/publications/pet_user_notes/pet_user_notes_v2_i1_may_1979.pdf|archive-date=2016-06-11|url-status=live}}</ref>
| 172.5 KB<ref name="progPET">{{cite book|title=Programming the PET/CBM: The Reference Encyclopedia For Commodore PET & CBM Users|last=West|first=Raeto Collin|page=167|publisher=COMPUTE! Books|isbn=0-942386-04-3|date=January 1982|url=https://archive.org/details/COMPUTEs_Programming_the_PET-CBM_1982_Small_Systems_Services/page/n175|access-date=2018-10-07}}</ref>
| 170 KB
|-
| style="text-align: left" | 5¼-inch [[Commodore DOS]] 2.1 (SSDD)
| style="text-align: center" | 1980<ref>{{cite web|url=https://github.com/mist64/cbmsrc/blob/master/DOS_4040/dos|title=cbmsrc / DOS_4040 / dos |website=[[GitHub]]|date=1980-02-05|access-date=2018-10-07}}</ref>
| 170.75 KB<ref name="progPET"/>
| 170 KB
|-
| style="text-align: left" | 5¼-inch Apple Disk II (DOS 3.3)
| style="text-align: center" | 1980
| 140 KB (256 byte sectors, 16 sectors/track, 35 tracks)
| 140 KB
|-
| style="text-align: left" | 5¼-inch Apple Disk II ([http://www.mobygames.com/developer/sheet/view/developerId,16399/ Roland Gustafsson]'s [http://fabiensanglard.net/prince_of_persia/pop_boot.php RWTS18])
| style="text-align: center" | 1988
| 157.5 KB (768 byte sectors, 6 sectors/track, 35 tracks)
| Capacity not marketed (game publisher's privately-contracted third-party custom DOS).
|-
| style="text-align: left" |5¼-inch Victor 9000 / ACT Sirius 1 (SSDD)
| style="text-align: center" | 1982<ref name="auto">{{cite web|url=http://bitsavers.org/pdf/victor/victor9000/Victor_9000_Hardware_Reference_Manual_1983.pdf |title=Victor 9000 Hardware Reference Manual |access-date=2022-09-12 | archive-url=https://web.archive.org/web/20220129140512/http://bitsavers.org/pdf/victor/victor9000/Victor_9000_Hardware_Reference_Manual_1983.pdf | archive-date=2022-01-29 |url-status=live}}</ref>
| 612 KB (512 byte sectors, 11–19 variable sectors / track, 80 tracks)
| 600 KB
|-
| style="text-align: left" |5¼-inch Victor 9000 / ACT Sirius 1 (DSDD)
| style="text-align: center" | 1982<ref name="auto"/>
| 1,196 KB (512 byte sectors, 11–19 variable sectors / track, 80 tracks)
| 1,200 KB
|-
| style="text-align: left" | 3½-inch HP SS
| style="text-align: center" | 1982
| 280 KB (256 byte sectors, 16 sectors/track, 70 tracks)
| 264 KB
|-
| style="text-align: left" | 5¼-inch Atari DOS 3
| style="text-align: center" | 1983
| 127 KB (128 byte sectors, 26 sectors/track, 40 tracks)
| 130 KB
|-
| style="text-align: left" | 3-inch
| style="text-align: center" | 1982<ref name="Amdisk-3MF">{{cite web |url=http://nikkicox.tripod.com/comp1981.htm |title=Chronology of Events in the History of Microcomputers − 1981–1983 Business Takes Over |access-date=2008-10-04 |archive-url=https://web.archive.org/web/20081207112541/http://nikkicox.tripod.com/comp1981.htm |archive-date=2008-12-07 |url-status=live}}</ref><ref name="3inch">{{cite web|title=Three-inch floppy disk product announced|url=http://csdl.computer.org/plugins/dl/pdf/mags/mi/1982/02/04070788.pdf|url-status=dead|archive-url=https://web.archive.org/web/20120808174200/http://csdl.computer.org/plugins/dl/pdf/mags/mi/1982/02/04070788.pdf|archive-date=2012-08-08|access-date=2008-10-04}}</ref>
| ?
| 125 KB (SS/SD),<br>500&nbsp;KB (DS/DD)<ref name="3inch"/>
|-
| style="text-align: left" | 3½-inch SS DD (at release)
| style="text-align: center" | 1983 <!-- see discussion at Talk%3AFloppy_disk#First_3½-inch_FDDs -->
| 360 KB (400&nbsp;KB on Macintosh)
| 500 KB
|-
| style="text-align: left" | 3½-inch DS DD
| style="text-align: center" | 1983 <!-- see discussion at Talk%3AFloppy_disk#First_3½-inch_FDDs -->
| 720 KB (800&nbsp;KB on Macintosh and [[RISC OS]],<ref name="RISC OS">{{cite web |url=https://www.riscos.com/support/users/userguide3/book1b/c_2.html |title=6. Using floppy and hard discs |work=RISC OS 3.7 User Guide |date=January 21, 1997 |access-date=January 4, 2022 }}{{Dead link|date=March 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> 880&nbsp;KB on [[Amiga]])
| 1&nbsp;MB
|-
| style="text-align: left" | 5¼-inch QD
| style="text-align: center" | 1980<ref>{{cite book |last=Porter |first=James |date=December 1982 |title=1982 Disk/Trend Report – Flexible Disk Drives |publisher=Disk/Trend |page=DT13-3 |quote=The original 48 tpi drives were joined by 96tpi drives from Tandon, Micro Peripherals and Micropolis in 1980 ...}}</ref>
| 720 KB
| 720 KB
|-
| style="text-align: left" | 5¼-inch RX50 (SSQD)
| style="text-align: center" | {{Circa|1982}}
| {{n/a}}
| 400 KB
|-
| style="text-align: left" | 5¼-inch HD
| style="text-align: center" | 1982<ref>1986 Disk/Trend Report, Flexible Disk Drives</ref>
| 1,200 KB
| 1.2&nbsp;MB
|-
| style="text-align: left" | 3-inch Mitsumi Quick Disk
| style="text-align: center" | 1985
| 128 to 256&nbsp;KB
| ?
|-
| style="text-align: left" | 3-inch [[Famicom Disk System]] (derived from Quick Disk)
| style="text-align: center" | 1986
| 112 KB
| 128&nbsp;KB<ref name="Revisiting the Famicom Disk System">{{cite web |url=https://www.eurogamer.net/articles/digitalfoundry-2019-retro-revisiting-famicom-disk-system |title=Revisiting the Famicom Disk System |website=[[Eurogamer]] |date=27 July 2019}}</ref>
|-
| style="text-align: left" | 2-inch
| style="text-align: center" | 1989
| 720 KB<ref name="InfoWorld July 1989">{{cite journal |title=Viability of 2-Inch Media Standard for PCs in Doubt |journal=[[InfoWorld]] |volume=11 |issue=31 |page=21 |date=1989-07-31 |url=https://books.google.com/books?id=tjAEAAAAMBAJ&pg=PT20}}</ref>
| ?
|-
| style="text-align: left" | 2½-inch Sharp CE-1600F,<ref name="Sharp_1986_CE1600F"/> CE-140F<br>(chassis: FDU-250, medium: CE-1650F)<ref name="Sharp_1986_CE140F"/>
| style="text-align: center" | 1986<ref name="Sharp_1986_CE1600F">{{cite book |title=Sharp PC-1600 Service Manual |chapter=Model CE-1600F |pages=98–104 |date=July 1986 |publisher=[[Sharp Corporation]], Information Systems Group, Quality & Reliability Control Center |location=Yamatokoriyama, Japan |chapter-url=http://sharppocketcomputers.com/4HK7JnFJDuVm/Service/ce1600f_service_manual.pdf |access-date=2017-03-12 |url-status=live |archive-url=https://web.archive.org/web/20170323132153/http://sharppocketcomputers.com/4HK7JnFJDuVm/Service/ce1600f_service_manual.pdf |archive-date=2017-03-23}}</ref><ref name="Sharp_1986_CE140F">{{cite book |title=Sharp Service Manual Model CE-140F Pocket Disk Drive |publisher=[[Sharp Corporation]] |id=00ZCE140F/SME |url=http://pockemul.free.fr/Documents/ce-140f_Service_manual.pdf |access-date=2017-03-11 |url-status=live |archive-url=https://web.archive.org/web/20170311145818/http://pockemul.free.fr/Documents/ce-140f_Service_manual.pdf |archive-date=2017-03-11}}</ref><ref name="1986_maxell_drives"/>
| [[flippy disk|Turnable]] diskette with 62,464 bytes per side<br>(512 byte sectors, 8 sectors/track, 16 tracks, [[GCR (4/5)]] recording)<ref name="Sharp_1986_CE1600F"/><ref name="Sharp_1986_CE140F"/>
| 2× 64 KB (128&nbsp;KB)<ref name="Sharp_1986_CE1600F"/><ref name="Sharp_1986_CE140F"/>
|-
| style="text-align: left" | 5¼-inch<ref>{{Cite patent|title=Production of perpendicular magnetic recording medium|fdate=1986-08-12|pubdate=1988-02-25|country=JP|number=S6344319A|inventor1-first= Osamu |inventor1-last=Kitagami |inventor2-first= Hideo |inventor2-last=Fujiwara|assign=[[Hitachi Maxell]]}}</ref> Perpendicular
| style="text-align: center" | 1986<ref name="1986_maxell_drives">{{cite magazine|last=Bateman|first=Selby|magazine=COMPUTE!|issue=70|date=March 1986|page=18|url=http://www.atarimagazines.com/compute/issue70/054_1_THE_FUTURE_OF_MASS_STORAGE.php|title=The Future of Mass Storage|publisher=COMPUTE! Publications, Inc.|access-date=2018-10-07|archive-url=https://web.archive.org/web/20180701002021/https://www.atarimagazines.com/compute/issue70/054_1_THE_FUTURE_OF_MASS_STORAGE.php|archive-date=2018-07-01|url-status=live}}</ref>
| 100 KB per inch<ref name="1986_maxell_drives"/>
| ?
|-
| style="text-align: left" | 3½-inch HD
| style="text-align: center" | 1986<ref name="InfoWorld November 1986">{{cite journal |title=Vendor Introduces Ultra High-Density Floppy Disk Media |journal=[[InfoWorld]] |volume=8 |issue=45 |page=19 |date=1986-11-10 |url=https://books.google.com/books?id=rDwEAAAAMBAJ&pg=PA19}}</ref>
| 1,440 KB (512 bytes sectors, 18 sectors/track, 160 tracks); 1,760&nbsp;KB on Amiga
| 1.44&nbsp;MB (2.0&nbsp;MB unformatted)
|-
| style="text-align: left" | 3½-inch HD
| style="text-align: center" | 1987
| 1,600 KB on RISC OS<ref name="RISC OS"/>
| 1.6&nbsp;MB
|-
| style="text-align: left" | 3½-inch ED
| style="text-align: center" | 1987<ref name="Mueller">{{cite book |title=Upgrading and Repairing PCs, 15th Anniversary Edition |last=Mueller |first=Scott |date=2004 |publisher=[[Que Publishing]] |isbn=0-7897-2974-1 |page=1380 |url=https://books.google.com/books?id=E1p2FDL7P5QC&pg=PA1380 |access-date=2011-07-16}}</ref>
| 2,880 KB (3,200&nbsp;KB on Sinclair QL)
| 2.88&nbsp;MB
|-
| style="text-align: left" | 3½-inch [[Floptical]] (LS)
| style="text-align: center" | 1991
| 20,385 KB
| 21&nbsp;MB
|-
| style="text-align: left" | 3½-inch [[SuperDisk]] (LS-120)
| style="text-align: center" | 1996
| 120,375&nbsp;KB
| 120&nbsp;MB
|-
| style="text-align: left" | 3½-inch [[SuperDisk]] (LS-240)
| style="text-align: center" | 1997
| 240,750&nbsp;KB
| 240&nbsp;MB
|-
| style="text-align: left" | 3½-inch [[HiFD]]
| style="text-align: center" | 1998/99
| ?
| 150/200&nbsp;MB
|-
| colspan=4 style="text-align: center" | Abbreviations: {{nowrap|1='''SD''' = Single Density;}} {{nowrap|1='''DD''' = Double Density;}} {{nowrap|1='''QD''' = Quad Density;}} {{nowrap|1='''HD''' = High Density;}} {{nowrap|1='''ED''' = Extra-high Density;}}<ref>{{cite book |title=Hardware-Praxis – PCs warten reparieren, aufrüsten und konfigurieren |last=Mueller |first=Scott |date=1994 |isbn=3-89319-705-2 |page=441 |edition=3rd |publisher=[[Addison-Wesley Publishing Company]] |language=de}}</ref><ref>{{cite magazine |last=Nelson |first=Jeanne |title=GSI card, drive let you use extra-high-density floppies |url=https://books.google.com/books?id=1T0EAAAAMBAJ&pg=PA101 |magazine=InfoWorld |date=14 October 1991 |publisher=InfoWorld Media Group, Inc. |via=Google Books}}</ref><ref name="Intel_1992_82077SL">{{cite book |last=Shah |first=Katen A. |date=1996 |title=Intel 82077SL for Super-Dense Floppies |publisher=[[Intel Corporation]], IMD Marketing |orig-year=September 1992, April 1992 |edition=2 |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>{{cite magazine |author=<!-- not stated --> |title=IBM PS/2 Model 57 SX |url=https://books.google.com/books?id=x2kb8n32nTMC&pg=PT38 |magazine=PC Mag |date=10 September 1991 |publisher=Ziff Davis, Inc. |via=Google Books}}</ref><ref>{{cite magazine |last=Nakamura |first=Roxanna Li |title=Extra-High Density 3½-Inch Disks Let Add-On Microfloppy Deliver in a Big Way |url=https://books.google.com/books?id=KjsEAAAAMBAJ&pg=PT22 |magazine=InfoWorld |date=19 March 1990 |publisher=InfoWorld Media Group, Inc. |via=Google Books}}</ref> {{nowrap|1='''LS''' = Laser Servo;}} {{nowrap|1='''HiFD''' = High capacity Floppy Disk;}} {{nowrap|1='''SS''' = Single Sided;}} {{nowrap|1='''DS''' = Double Sided}}
|-
| colspan=4 style="text-align: left" | Formatted storage capacity is total size of all sectors on the disk:

* For 8-inch see ''[[List of floppy disk formats#IBM 8-inch formats]]''. Spare, hidden and otherwise reserved sectors are included in this number.
* For 5¼- and 3½-inch capacities quoted are from subsystem or system vendor statements.

Marketed capacity is the capacity, typically unformatted, by the original media OEM vendor or in the case of IBM media, the first OEM thereafter. Other formats may get more or less capacity from the same drives and disks.
|}

[[File:Box of floppy disks and USB memory stick.jpg|thumb|right|The USB stick under the two boxes of about 80 floppy disks is capable of holding over 130 times as much data as the two boxes of disks put together.]]
Data is generally written to floppy disks in sectors (angular blocks) and tracks (concentric rings at a constant radius). For example, the HD format of 3½-inch floppy disks uses 512 bytes per sector, 18 sectors per track, 80 tracks per side and two sides, for a total of 1,474,560 bytes per disk.<ref>{{cite web |url=http://www.lintech.org/comp-per/08FDK.pdf |title=Chapter 8: Floppy Disk Drives |access-date=2011-07-16 |archive-url=https://web.archive.org/web/20120127200411/http://www.lintech.org/comp-per/08FDK.pdf |archive-date=2012-01-27 |url-status=live}}</ref>{{failed verification|reason=Article cited lacks the information stated.|date=August 2020}} Some disk controllers can vary these parameters at the user's request, increasing storage on the disk, although they may not be able to be read on machines with other controllers. For example, [[Microsoft]] applications were often distributed on 3½-inch 1.68&nbsp;MB [[Distribution Media Format|DMF]] disks formatted with 21 sectors instead of 18; they could still be recognized by a standard controller. On the [[IBM PC]], [[MSX]] and most other microcomputer platforms, disks were written using a [[constant angular velocity]] (CAV) format,<ref name="Mueller"/> with the disk spinning at a constant speed and the sectors holding the same amount of information on each track regardless of radial location.{{fact|date=June 2024}}

Because the sectors have constant angular size, the 512 bytes in each sector are compressed more near the disk's center. A more space-efficient technique would be to increase the number of sectors per track toward the outer edge of the disk, from 18 to 30 for instance, thereby keeping nearly constant the amount of physical disk space used for storing each sector; an example is [[zone bit recording]]. Apple implemented this in early Macintosh computers by spinning the disk more slowly when the head was at the edge, while maintaining the data rate, allowing 400&nbsp;KB of storage per side and an extra 80&nbsp;KB on a double-sided disk.<ref>{{cite web |title= The Original Macintosh |url= http://www.folklore.org/ProjectView.py?project=Macintosh&index=75&sortOrder=Sort%20by%20Date&detail=high |access-date=2013-12-03 | work = Folklore |archive-url= https://web.archive.org/web/20131205100719/http://www.folklore.org/ProjectView.py?project=Macintosh&index=75&sortOrder=Sort%20by%20Date&detail=high |archive-date= 2013-12-05 |url-status=live}}</ref> This higher capacity came with a disadvantage: the format used a unique drive mechanism and control circuitry, meaning that Mac disks could not be read on other computers. Apple eventually reverted to constant angular velocity on HD floppy disks with their later machines, still unique to Apple as they supported the older variable-speed formats.{{fact|date=June 2024}}

[[Disk formatting]] is usually done by a utility program supplied by the computer [[operating system|OS]] manufacturer; generally, it sets up a file storage directory system on the disk, and initializes its sectors and tracks. Areas of the disk unusable for storage due to flaws can be locked (marked as "bad sectors") so that the operating system does not attempt to use them. This was time-consuming so many environments had quick formatting which skipped the error checking process. When floppy disks were often used, disks pre-formatted for popular computers were sold. The unformatted capacity of a floppy disk does not include the sector and track headings of a formatted disk; the difference in storage between them depends on the drive's application. Floppy disk drive and media manufacturers specify the unformatted capacity (for example, 2&nbsp;MB for a standard 3½-inch HD floppy). It is implied that this should not be exceeded, since doing so will most likely result in performance problems. [[Distribution Media Format|DMF]] was introduced permitting 1.68&nbsp;MB to fit onto an otherwise standard 3½-inch disk; utilities then appeared allowing disks to be formatted as such.{{fact|date=June 2024}}

[[Binary prefix#Floppy drives|Mixtures]] of decimal prefixes and binary sector sizes require care to properly calculate total capacity. Whereas semiconductor memory naturally favors powers of two (size doubles each time an address pin is added to the integrated circuit), the capacity of a disk drive is the product of sector size, sectors per track, tracks per side and sides (which in hard disk drives with multiple platters can be greater than 2). Although other sector sizes have been known in the past, formatted sector sizes are now almost always set to powers of two (256 bytes, 512 bytes, etc.), and, in some cases, disk capacity is calculated as multiples of the sector size rather than only in bytes, leading to a combination of decimal multiples of sectors and binary sector sizes. For example, 1.44&nbsp;MB 3½-inch HD disks have the "M" prefix peculiar to their context, coming from their capacity of 2,880 512-byte sectors (1,440&nbsp;KiB), consistent with neither a decimal [[megabyte]] nor a binary [[mebibyte]] (MiB). Hence, these disks hold 1.47&nbsp;MB or 1.41&nbsp;MiB. Usable data capacity is a function of the disk format used, which in turn is determined by the FDD controller and its settings. Differences between such formats can result in capacities ranging from approximately 1,300 to 1,760&nbsp;KiB (1.80&nbsp;MB) on a standard 3½-inch high-density floppy (and up to nearly 2&nbsp;MB with utilities such as 2M/2MGUI). The highest capacity techniques require much tighter matching of drive head geometry between drives, something not always possible and unreliable. For example, the [[LS-240]] drive supports a 32&nbsp;MB capacity on standard 3½-inch HD disks,<ref>{{cite web |title=Properties of Storage Systems |url= http://www.mtsac.edu/~rpatters/CISB11/Chapters/Chapter_03/Chap03/LectureMain.htm |publisher=Mt. San Antonio College |url-status= dead |archive-url= https://web.archive.org/web/20131207142330/http://www.mtsac.edu/~rpatters/CISB11/Chapters/Chapter_03/Chap03/LectureMain.htm |archive-date= 2013-12-07}}</ref> but this is a write-once technique, and requires its own drive.{{fact|date=June 2024}}

The raw maximum transfer rate of 3½-inch ED floppy drives (2.88&nbsp;MB) is nominally 1,000&nbsp;[[kilobit]]s/s, or approximately 83% that of single-speed CD‑ROM (71% of audio CD). This represents the speed of raw data bits moving under the read head; however, the effective speed is somewhat less due to space used for headers, gaps and other format fields and can be even further reduced by delays to seek between tracks.{{fact|date=June 2024}}