Editing Floppy disk (section)

===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}}