Floppy disk

Industry observers categorize floppy disks and floppy disk drives according to size and capacity with four major categories being , , and high-capacity floppy disks and floppy disk drives. , and drives were manufactured in a variety of sizes, most to fit standardized drive bays. Alongside the common disk sizes were non-classical sizes for specialized systems. == History ==

8-inch The first commercial floppy disks, developed in the late 1960s, were in diameter; None of these ever reached the point where it could be assumed that every current PC would have one, and they were later largely replaced first by optical disc burners and then by flash storage. In 1990, an attempt was made to standardize details for a 20MB 3½-inch format floppy. At the time, "three different technologies that are not interchangeable" existed. One major goal was that the to-be-developed standard drive be backward compatible: that it be able to read 720 KB and 1.44 MB floppies. Variants Other smaller floppy sizes were proposed, especially for portable or pocket-sized devices that needed a smaller storage device. • 3¼-inch floppies otherwise similar to 5¼-inch floppies were proposed by Tabor and Dysan. • Three-inch disks similar in construction to 3½-inch were manufactured and used for a time, particularly by 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. Use in Japan's government ended in 2024. Windows 10 and Windows 11 no longer come with drivers for floppy disk drives (both internal and external). However, they will still support them with a separate device driver provided by Microsoft. The British Airways Boeing 747-400 fleet, up to its retirement in 2020, used 3½-inch floppy disks to load avionics software. Sony, who had been in the floppy disk business since 1983, ended domestic sales of all six 3½-inch floppy disk models as of March 2011. This has been viewed by some as the end of the floppy disk. While production of new floppy disk media has ceased, sales and uses of this media from inventories is expected to continue until at least 2026. == Structure ==

8-inch and 5¼-inch disks 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. • Zip disk : Physically both the media and cartridge were slightly larger but similar to other 3½-inch media and cartridges. A linear actuator positioned flying heads over high-capacity media that started at 100 MB and grew to 700 MB. It was offered in a variety of interfaces including PATA. • LS-120/LS-240 :LS, for LASER-servo, uses a LED to generate light that allows the drive to align its heads on high capacity FD media, initially at 120 MB and subsequently at 240 MB. The drive read and write 3½-inch 1,440 KB floppy disks, and some versions of the drive can write 32 MB onto a 3½-inch 1,440 kB disk albeit not too reliably. It was offered in a variety of interfaces including PATA. • Sony HiFD : Structurally similar to the Floptical and initially at 150 MB, it was removed from the market and subsequently reintroduced at 200 MB • Caleb UHD144 : Structurally similar to the Floptical it provides 144 MB of storage and is capable reading and writing 720 kB and 1.44 MB 3½-inch disks. Variants In addition to the four generations of floppy disks and drives covered in this article there were various other floppy disks (and drives) offered, some were failed attempts to establish a standard for a generation while others were for special applications. == Operation ==

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. 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. Formatting 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 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. 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. Some errors are soft and can be resolved by re-trying the read operation; other errors are permanent and will signal a failure to the operating system if multiple attempts to read the data still fail Insertion and ejection After a disk is inserted, a catch or lever mechanism engages 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 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 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 On 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 have soft-eject 3½-inch disk drives as well for which PC DOS 5.02 and higher includes an EJECT command. Finding track zero Before a disk can be accessed, the drive needs to synchronize its head position with the disk tracks. 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. Drives without a sensor such as the Apple II mechanism attempt 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. This physical striking is responsible for drive clicking during the boot and when disk errors occurred and track zero synchronization was attempted. Finding sectors All 8-inch and some 5¼-inch drives use methods to locate sectors, known as either hard sectors or soft sectors, with the small hole in the jacket, off to the side of the spindle hole, used for timing reference. A light beam sensor detects when a punched hole in the disk is visible through the hole in the jacket. For a soft-sectored disk, there is only a single hole, which is used to locate the first sector of each track. 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. 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. 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. In order to fit more data onto a disk, some 3½-inch drives (notably the Macintosh External 400K and 800K drives) instead use constant linear velocity, 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. == Historical sequence of floppy disk formats ==

Floppy disk size is often referred to in inches, even in countries using 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 mm is closer to 3.54 inches. Formatted capacities are generally set in terms of kilobytes and megabytes. 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. 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 MB DMF disks formatted with 21 sectors instead of 18; they could still be recognized by a standard controller. Constant linear velocity was generally not used on floppy disks, so most computer systems used constant angular velocity (CAV) format, with the disk spinning at a constant speed and the sectors holding the same amount of information on each track regardless of radial location. A notable exception was Apple, which implemented CLV in early Macintosh computers by spinning the disk more slowly when the head was at the edge, while maintaining the data rate, allowing 400 KB of storage per side and an extra 80 KB on a double-sided disk. 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 KB of storage per side and an extra 80 KB on a double-sided disk. 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. Disk formatting is usually done by a utility program supplied by the computer 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 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. DMF was introduced permitting 1.68 MB to fit onto an otherwise standard 3½-inch disk; utilities then appeared allowing disks to be formatted as such. Mixtures of decimal prefixes and binary sector sizes require care to properly calculate total capacity. For example, 1.44 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 KiB), consistent with neither a decimal megabyte nor a binary mebibyte (MiB). Hence, these disks hold 1.47 MB or 1.41 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 KiB (1.80 MB) on a standard 3½-inch high-density floppy (and up to nearly 2 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 MB capacity on standard 3½-inch HD disks, but this is a write-once technique, and requires its own drive. The raw maximum transfer rate of 3½-inch ED floppy drives (2.88 MB) is nominally 1,000 kilobits/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. == Adoption and usage ==

USB floppy drive, model 01946: an external drive that accepts high-density disks Floppy disks became commonplace during the 1980s and 1990s in their use with personal computers to distribute software, transfer data, and create backups. Before hard disks became affordable to the general population, floppy disks were often used to store a computer's operating system (OS). Most home computers from that time have an elementary OS and BASIC stored in read-only memory (ROM), with the option of loading a more advanced OS from a floppy disk. By the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were an estimated five billion standard floppy disks in use. An attempt to enhance the existing 3½-inch designs was the SuperDisk in the late 1990s, using very narrow data tracks and a high precision head guidance mechanism with a capacity of 120 MB and backward-compatibility with standard 3½-inch floppies; a format war briefly occurred between SuperDisk and other high-density floppy-disk products, although ultimately recordable CDs/DVDs, solid-state flash storage, and eventually cloud-based online storage would render all these removable disk formats obsolete. External USB-based floppy disk drives are still available, and many modern systems provide firmware support for booting from such drives. == Legacy ==

For more than two decades, the floppy disk was the primary external writable storage device used. Most small computing environments before the 1990s were non-networked, and floppy disks were the primary means to transfer data between such computers, a method known informally as sneakernet. Unlike hard disks, floppy disks were more commonly handled and seen, and typically novice users could identify a floppy disk. Because of these factors, a picture of a 3½-inch floppy disk became an interface metaphor for saving data. , the floppy disk symbol is still used by software on user-interface elements related to saving files even though physical floppy disks are largely obsolete. Examples of such software include LibreOffice, Microsoft Paint, and WordPad. It is present in many UI symbol libraries and has a Unicode code point 💾 since 2010. == See also ==