Editing Floppy disk (section)

==Design==
===Structure===
====8-inch and 5¼-inch disks====
[[File:8-inch floppy disk - IZOT, Bulgaria - inside.jpg|right|thumb|The inside of a destructively disassembled 8-inch floppy disk]]
[[File:Squareholepunch2.png|thumb|upright|A disk notcher punch, which could make read-only 5¼" floppies writable, and [[flippy disk|convert certain single-sided 5¼-inch diskettes to double-sided]], by adding cutouts which drives use to determine if the disk is writable.]]
The 8-inch and 5¼-inch floppy disks contain a magnetically coated round plastic medium with a large circular hole in the center for a drive's spindle. The medium is contained in a square plastic cover that has a small oblong opening in both sides to allow the drive's heads to read and write data and a large hole in the center to allow the magnetic medium to spin by rotating it from its middle hole.<ref>{{Cite web |date=2024-03-06 |title=What is a Floppy Disk? |url=https://www.geeksforgeeks.org/what-is-a-floppy-disk/ |access-date=2025-01-26 |website=GeeksforGeeks |language=en-US}}</ref>

Inside the cover are two layers of fabric with the magnetic medium sandwiched in the middle. The fabric is designed to reduce friction between the medium and the outer cover, and catch particles of debris abraded off the disk to keep them from accumulating on the heads. The cover is usually a one-part sheet, double-folded with flaps glued or spot-welded together.<ref>{{cite web |title=What is a Floppy Disk? Definition, Advantages & Disadvantages |url=https://study.com/academy/lesson/what-is-floppy-disk-definition-advantages-disadvantages.html |website=Study.com |access-date=February 22, 2025}}</ref>

A small notch on the side of the disk identifies whether it is writable, as detected by a mechanical switch or [[photoelectric sensor]]. In the 8-inch disk, the notch being covered or not present enables writing, while in the 5¼-inch disk, the notch being present and uncovered enables writing. Tape may be used over the notch to change the mode of the disk. Punch devices were sold to convert read-only 5¼" disks to writable ones, and also to enable writing on the unused side of single-sided disks for computers with single-sided drives. The latter worked because single- and double-sided disks typically contained essentially identical actual magnetic media, for manufacturing efficiency. Disks whose obverse and reverse sides were thus used separately in single-sided drives were known as [[flippy disk]]s. Disk notching 5¼" floppies for PCs was generally only required where users wanted to overwrite original 5¼" disks of store-bought software, which somewhat commonly shipped with no notch present.<ref>{{cite web |title=Write Protect Notch |url=https://www.pcmag.com/encyclopedia/term/write-protect-notch |website=PCMag Encyclopedia |access-date=February 22, 2025}}</ref>

Another LED/photo-transistor pair located near the center of the disk detects the ''index hole'' once per rotation in the magnetic disk. Detection occurs whenever the drive's sensor, the holes in the correctly inserted floppy's plastic envelope and a single hole in the rotating floppy disk medium line up. This mechanism is used to detect the angular start of each track, and whether or not the disk is rotating at the correct speed. Early 8‑inch and 5¼‑inch disks also had holes for each sector in the enclosed magnetic medium, in addition to the index hole,<ref>{{cite web | url=https://retrocmp.de/fdd/diskette/diskette.htm#hardsoft | title=Floppy Disk / Diskettes // Retrocmp / Retro computing }}</ref> with the same [[radius|radial distance]] from the center, for alignment with the same envelope hole. These were termed ''[[hard sectoring|hard sectored]]'' disks. Later ''soft-[[Disk sector|sectored]]'' disks have only one index hole in the medium, and sector position is determined by the disk controller or low-level software from patterns marking the start of a sector. Generally, the same drives are used to read and write both types of disks, with only the disks and controllers differing. Some operating systems using soft sectors, such as [[Apple DOS]], do not use the index hole, and the drives designed for such systems often lack the corresponding sensor; this was mainly a hardware cost-saving measure.<ref>{{cite web |url=https://apple2history.org/history/ah05/ |title=The Disk II |date=2008-12-02 |website=Apple II History |access-date=2018-02-17 |quote=Wozniak's technique would allow the drive to do self-synchronization ("soft sectoring"), not have to deal with that little timing hole, and save on hardware. |url-status=dead |archive-url=https://web.archive.org/web/20180219091809/https://apple2history.org/history/ah05/ |archive-date=2018-02-19}}</ref>

====3½-inch disk====
[[File:Back of floppy disk with transparent case.jpg|thumb|Rear side of a 3½-inch floppy disk in a transparent case, showing its internal parts]]

The core of the 3½-inch disk is the same as the other two disks, but the front has only a label and a small opening for reading and writing data, protected by the shutter—a spring-loaded metal or plastic cover, pushed to the side on entry into the drive. Rather than having a hole in the center, it has a metal hub which mates to the spindle of the drive. Typical 3½-inch disk magnetic coating materials are:<ref name="SCS_2007">{{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=de |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}}</ref>

* DD: 2&nbsp;μm magnetic [[iron oxide]]
* HD: 1.2&nbsp;μm [[cobalt]]-doped iron oxide
* ED: 3&nbsp;μm [[barium ferrite]]{{fact|date=June 2024}}

Two holes at the bottom left and right indicate whether the disk is write-protected and whether it is high-density; these holes are spaced as far apart as the holes in punched [[A4 paper size|A4]] paper, allowing write-protected high-density floppy disks to be clipped into international standard ([[ISO 838]]) [[ring binder]]s. The dimensions of the disk shell are not quite square: its width is slightly less than its depth, so that it is impossible to insert the disk into a drive slot sideways (i.e. rotated 90 degrees from the correct shutter-first orientation). A diagonal notch at top right ensures that the disk is inserted into the drive in the correct orientation—not upside down or label-end first—and an arrow at top left indicates direction of insertion. The drive usually has a button that, when pressed, ejects the disk with varying degrees of force, the discrepancy due to the ejection force provided by the spring of the shutter. In [[MSX]], [[IBM PC compatible]]s, Commodores, Apple II/[[Apple III|IIIs]], and other non-Apple-Macintosh machines with standard floppy disk drives, a disk may be ejected manually at any time. The drive has a disk-change switch that detects when a disk is ejected or inserted. Failure of this mechanical switch is a common source of disk corruption if a disk is changed and the drive (and hence the operating system) fails to notice.{{fact|date=June 2024}}

One of the chief [[usability]] problems of the floppy disk is its vulnerability; even inside a closed plastic housing, the disk medium is highly sensitive to dust, condensation and temperature extremes. As with all [[magnetic storage]], it is vulnerable to magnetic fields. Blank disks have been distributed with an extensive set of warnings, cautioning the user not to expose it to dangerous conditions. Rough treatment or removing the disk from the drive while the magnetic media is still spinning is likely to cause damage to the disk, drive head, or stored data. On the other hand, the 3½‑inch floppy disk has been lauded for its mechanical usability by [[human–computer interaction]] expert [[Donald Norman]]:<ref>{{cite book |author-link=Donald Norman |first=Donald |last=Norman |title=The Design of Everyday Things |chapter=Chapter 1 |date=1990 |isbn=0-385-26774-6 |publisher=[[Doubleday (publisher)|Doubleday]] |location=New York, US|title-link=The Design of Everyday Things}}</ref>

{{blockquote
| A simple example of a good design is the 3½-inch magnetic diskette for computers, a small circle of floppy magnetic material encased in hard plastic. Earlier types of floppy disks did not have this plastic case, which protects the magnetic material from abuse and damage. A sliding metal cover protects the delicate magnetic surface when the diskette is not in use and automatically opens when the diskette is inserted into the computer. The diskette has a square shape: there are apparently eight possible ways to insert it into the machine, only one of which is correct. What happens if I do it wrong? I try inserting the disk sideways. Ah, the designer thought of that. A little study shows that the case really isn't square: it's rectangular, so you can't insert a longer side. I try backward. The diskette goes in only part of the way. Small protrusions, indentations, and cutouts prevent the diskette from being inserted backward or upside down: of the eight ways one might try to insert the diskette, only one is correct, and only that one will fit. An excellent design.
}}

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[[File:Floppy drive spindle motor open.jpg|thumb|left|The spindle motor from a 3½‑inch unit]]
[[File:Citizen W1D-9364 - read write head-4005.jpg|thumb|A [[disk read-and-write head|read-write head]] from a 3½‑inch unit]]

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===Operation===
[[File:Lecteur de disquette 2.jpg|thumb|left|How the read-write head is applied on the floppy]]
{{listen
| pos          = right
| filename     = Floppy drive sounds.ogg
| title        = 3,5 inch floppy drive noises during a format
| description  = 00:00–00:03: Starting<br>
00:03–00:15: Normal operation<br>
00:15–00:27: Drive noises while the head passes over bad sectors
| format       = [[Ogg]]
}}

A spindle motor in the drive rotates the magnetic medium at a certain speed, while a stepper motor-operated mechanism moves the magnetic read/write heads radially along the surface of the disk. Both read and write operations require the media to be rotating and the head to contact the disk media, an action originally accomplished by a disk-load solenoid.<ref>{{cite web|date=2005|editor-last=Porter|editor-first=Jim|title=Oral History Panel on 8 inch Floppy Disk Drives|url=http://archive.computerhistory.org/resources/text/Oral_History/8_inch_Floppy_Drive/8_inch_Floppy_Drive.oral_history.2005.102657926.pdf|url-status=dead|archive-url=https://web.archive.org/web/20150513110507/http://archive.computerhistory.org/resources/text/Oral_History/8_inch_Floppy_Drive/8_inch_Floppy_Drive.oral_history.2005.102657926.pdf|archive-date=2015-05-13|access-date=2011-06-22|page=4}}</ref> Later drives held the heads out of contact until a front-panel lever was rotated (5¼-inch) or disk insertion was complete (3½-inch). To write data, current is sent through a coil in the head as the media rotates. The head's magnetic field aligns the magnetization of the particles directly below the head on the media. When the current is reversed the magnetization aligns in the opposite direction, encoding one bit of data. To read data, the magnetization of the particles in the media induce a tiny voltage in the head coil as they pass under it. This small signal is amplified and sent to the [[floppy disk controller]], which converts the streams of pulses from the media into data, checks it for errors, and sends it to the host computer system.{{fact|date=June 2024}}

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====Formatting====
{{Main|Disk formatting}}
[[File:Visualization of magnetic information on a Floppy Disk (CMOS-MagView).jpg|thumb|Visualization of magnetic information on floppy disk (image recorded with CMOS-MagView)]]
A blank unformatted diskette has a coating of magnetic oxide with no magnetic order to the particles. During formatting, the magnetizations of the particles are aligned forming tracks, each broken up into [[disk sector|sectors]], enabling the controller to properly read and write data. The tracks are concentric rings around the center, with spaces between tracks where no data is written; gaps with padding bytes are provided between the sectors and at the end of the track to allow for slight speed variations in the disk drive, and to permit better interoperability with disk drives connected to other similar systems.{{fact|date=June 2024}}

Each sector of data has a header that identifies the sector location on the disk. A [[cyclic redundancy check]] (CRC) is written into the sector headers and at the end of the user data so that the disk controller can detect potential errors.{{fact|date=June 2024}}

Some errors are [[soft error|soft]] and can be resolved by automatically re-trying the read operation; other errors are permanent and the disk controller will signal a failure to the operating system if multiple attempts to read the data still fail.{{fact|date=June 2024}}

====Insertion and ejection====
After a disk is inserted, a catch or lever at the front of the drive is manually lowered to prevent the disk from accidentally emerging, engage the spindle clamping hub, and in two-sided drives, engage the second read/write head with the media.{{fact|date=June 2024}}

In some 5¼-inch drives, insertion of the disk compresses and locks an ejection spring which partially ejects the disk upon opening the catch or lever. This enables a smaller concave area for the thumb and fingers to grasp the disk during removal.{{fact|date=June 2024}}

Newer 5¼-inch drives and all 3½-inch drives automatically engage the spindle and heads when a disk is inserted, doing the opposite with the press of the eject button.{{fact|date=June 2024}}

On Apple [[Mac (computer)|Macintosh]] computers with built-in 3½-inch disk drives, the ejection button is replaced by software controlling an ejection motor which only does so when the operating system no longer needs to access the drive. The user could drag the image of the floppy drive to the trash can on the desktop to eject the disk. In the case of a power failure or drive malfunction, a loaded disk can be removed manually by inserting a straightened [[paper clip]] into a small hole at the drive's front panel, just as one would do with a [[CD-ROM]] drive in a similar situation. The [[X68000]] has soft-eject 5¼-inch drives. Some late-generation [[IBM PS/2]] machines had soft-eject 3½-inch disk drives as well for which some issues of [[DOS]] (i.e. [[PC DOS 5.02]] and higher) offered an [[EJECT (DOS command)|EJECT]] command.{{fact|date=June 2024}}

====Finding track zero====
Before a disk can be accessed, the drive needs to synchronize its head position with the disk tracks. In some drives, this is accomplished with a Track Zero Sensor, while for others it involves the drive head striking an immobile reference surface.{{fact|date=June 2024}}

In either case, the head is moved so that it is approaching track zero position of the disk. When a drive with the sensor has reached track zero, the head stops moving immediately and is correctly aligned. For a drive without the sensor, the mechanism attempts to move the head the maximum possible number of positions needed to reach track zero, knowing that once this motion is complete, the head will be positioned over track zero.{{fact|date=June 2024}}

Some drive mechanisms such as the Apple II 5¼-inch drive without a track zero sensor, produce characteristic mechanical noises when trying to move the heads past the reference surface. This physical striking is responsible for the 5¼-inch drive clicking during the boot of an Apple II, and the loud rattles of its DOS and ProDOS when disk errors occurred and track zero synchronization was attempted.{{fact|date=June 2024}}

====Finding sectors====
All 8-inch and some 5¼-inch drives use a mechanical method to locate sectors, known as either ''hard sectors'' or ''soft sectors'', and is the purpose of the small hole in the jacket, off to the side of the spindle hole. A light beam sensor detects when a punched hole in the disk is visible through the hole in the jacket.{{fact|date=June 2024}}

For a soft-sectored disk, there is only a single hole, which is used to locate the first sector of each track. Clock timing is then used to find the other sectors behind it, which requires precise speed regulation of the drive motor.{{fact|date=June 2024}}

For a hard-sectored disk, there are many holes, one for each sector row, plus an additional hole in a half-sector position, that is used to indicate sector zero.{{fact|date=June 2024}}

The Apple II computer system is notable in that it does not have an index-hole sensor and ignores the presence of hard or soft sectoring. Instead, it uses special repeating data synchronization patterns written to the disk between each sector, to assist the computer in finding and synchronizing with the data in each track.<ref>{{cite book |last=Brenner |first=Robert C. |title=The Apple II Plus/IIe Troubleshooting & Repair Guide |year=1984 |publisher=Howard W. Sams & Co. |url=https://vintageapple.org/apple_ii/pdf/Apple_II_Plus_IIe_Troubleshooting_%26_Repair_Guide_1984.pdf}}</ref>

The later 3½-inch drives of the mid-1980s do not use sector index holes, but instead also use synchronization patterns.{{fact|date=June 2024}}

Most 3½-inch drives use a constant speed drive motor and contain the same number of sectors across all tracks. This is sometimes referred to as [[Constant Angular Velocity]] (CAV). In order to fit more data onto a disk, some 3½-inch drives (notably the [[Macintosh External Disk Drive|Macintosh External 400K and 800K drives]]) instead use [[Constant Linear Velocity]] (CLV), which uses a variable-speed drive motor that spins more slowly as the head moves away from the center of the disk, maintaining the same speed of the head(s) relative to the surface(s) of the disk. This allows more sectors to be written to the longer middle and outer tracks as the track length increases.{{fact|date=June 2024}}