A floppy disk is an increasingly obsolete data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. Floppy disks are read and written by a floppy disk drive or FDD, the initials of which should not be confused with "fixed disk drive", which is another term for an hard disk drive. Invented by IBM, floppy disks in 8-inch (200 mm), 5¼-inch (133⅓ mm), and the newest and most common 3½-inch (90 mm) formats enjoyed many years as a popular and ubiquitous form of data storage and exchange, from the mid-1970s to the late 1990s. They have now been superseded by flash and optical storage devices.
Before hard disks became affordable, floppy disks were often also used to store a computer's operating system (OS), in addition to application software and data. Most home computers had a primary OS (often BASIC) stored permanently in on-board ROM, with the option of loading a more advanced disk operating system from a floppy, whether it be a proprietary system, CP/M, or later, DOS.
By the early 1990s, the increasing size of software meant that many programs demanded multiple diskettes; a large package like Windows or Adobe Photoshop could use a dozen disks or more. Toward the end of the 1990s, distribution of larger packages therefore gradually switched to CD-ROM (or online distribution for smaller programs).
Mechanically incompatible higher-density formats were introduced (e.g. the Iomega Zip disk) and were briefly popular, but adoption was limited by the competition between proprietary formats, and the need to buy expensive drives for computers where the media would be used. In some cases, such as with the Zip drive, the failure in market penetration was exacerbated by the release of newer higher-capacity versions of the drive and media that were not forward-compatible with the original drives, thus fragmenting the user base between new users and early adopters who were unwilling to pay for an upgrade so soon. A chicken or the egg scenario ensued, with consumers wary of making costly investments into unproven and rapidly changing technologies, with the result that none of the technologies were able to prove themselves and stabilize their market presence. Soon, inexpensive recordable CDs with even greater capacity, which were also compatible with an existing infrastructure of CD-ROM drives, made the new floppy technologies redundant. The last advantage of floppy disks, reusability, was again countered by re-writable CDs. Later, advancements in flash-based devices and widespread adoption of the USB interface provided another alternative that, in turn, made even optical storage obsolete for some purposes.
An attempt to continue the traditional diskette was the SuperDisk (LS-120) in the late 1990s, with a capacity of 120 MB (actually 120.375 MB), which was backward compatible with standard 3½-inch floppies. For some time, PC manufacturers were reluctant to remove the floppy drive because many IT departments appreciated a built-in file transfer mechanism that always worked and required no device driver to operate properly. However, manufacturers and retailers have progressively reduced the availability of computers fitted with floppy drives and of the disks themselves.
External USB-based floppy disk drives are available for computers without floppy drives, and they work on any machine that supports USB Mass Storage Devices. Many modern systems even provide firmware support for booting to a USB-mounted floppy drive.
It should be noted that Windows XP still requires the use of floppy drives to install third-party RAID, SATA and AHCI hard drives, unless the install cd were modified to include these drivers with programs made to customize a Windows XP install cd, such as nLite. This requirement was only dropped with the introduction of Windows Vista in 2007. Most PC motherboards will still attempt to boot from a floppy drive, depending on CMOS settings.
|Disk format||Year introduced||Formatted|
(in kB = 1024 bytes if not stated)
|8-inch - IBM 23FD (read-only)||1971||79.7||?|
|8-inch - Memorex 650||1972||175 kB||1.5 megabit [unformatted]|
|8-inch - SSSD|
IBM 33FD / Shugart 901
|1973||237.25||3.1 Mbits unformatted|
|8-inch - DSSD|
IBM 43FD / Shugart 850
|1976||500.5||6.2 Mbits unformatted|
|5¼-inch (35 track)|
Shugart SA 400
|1976||89.6 kB||110 kB|
IBM 53FD / Shugart 850
- 1200 (MS-DOS FAT)
|5¼-inch DD||1978||360 or 800||360 KB|
HP single sided
|3-inch||1982||360||125 kB (SS/SD), 500 kB (DS/DD)|
|3½-inch (DD at release)||1984||720||720 KB|
|5¼-inch QD||720||720 KB|
|5¼-inch HD||1982 YE Data YD380||1,182,720 bytes||1.2 MB|
Mitsumi Quick Disk
|1985||128 to 256||?|
|5¼-inch Perpendicular||1986||100 MB||?|
|3½-inch HD||1987||1440||1.44 MB|
|3½-inch ED||1987||2880||2.88 MB|
|3½-inch Floptical (LS)||1991||21000||21 MB|
|3½-inch LS-120||1996||120.375 MB||120 MB|
|3½-inch LS-240||1997||240.75 MB||240 MB|
|3½-inch HiFD||1998/99||150/200 MB||150/200 MB|
|¹ The formatted capacities of floppy disks frequently corresponded only vaguely to their capacities as marketed by drive and media companies, due to differences between formatted and unformatted capacities and also due to the non-standard use of binary prefixes in labeling and advertising floppy media. The erroneous "1.44 MB" value for the 3½-inch HD floppies is the most widely known example. See reported storage capacity.|
|Dates and capacities marked ? are of unclear origin and need source information; other listed capacities refer to:|
Formatted Storage Capacity is total size of all sectors on the disk:
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.
The earliest floppy disks, invented at IBM, were 8 inches in diameter. They became commercially available in 1971. Disks in this form factor were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation.
In 1976 two of Shugart Associates’s employees, Jim Adkisson and Don Massaro, were approached by An Wang of Wang Laboratories, who felt that the 8-inch format was simply too large for the desktop word processing machines he was developing at the time. After meeting in a bar in Boston, Adkisson asked Wang what size he thought the disks should be, and Wang pointed to a napkin and said “about that size”. Adkisson and Massaro took the napkin back to California, found it to be 5¼ inches wide, and developed a new drive of this size storing 98.5 KB later increased to 110 KB by adding 5 tracks. The 5¼-inch drive was considerably less expensive than 8-inch drives from IBM, and soon started appearing on CP/M machines. At one point Shugart was producing 4,000 drives a day. By 1978 there were more than 10 manufacturers producing 5¼-inch floppy drives, in competing physical disk formats: hard-sectored (90 KB) and soft-sectored (110 KB). The 5¼-inch formats quickly displaced the 8-inch for most applications, and the 5¼-inch hard-sectored disk format eventually disappeared.
Throughout the early 1980s the limitations of the 5¼-inch format were starting to become clear. Originally designed to be smaller and more practical than the 8-inch format, the 5¼-inch system was itself too large, and as the quality of the recording media grew, the same amount of data could be placed on a smaller surface. Another problem was that the 5¼-inch disks were simply scaled down versions of the 8-inch disks, which had never really been engineered for ease of use. The thin folded-plastic shell allowed the disk to be easily damaged through bending, and allowed dirt to get onto the disk surface through the opening.
A number of solutions were developed, with drives at 2-inch, 2½-inch, 3-inch and 3½-inch (50, 60, 75 and 90 mm) all being offered by various companies. They all shared a number of advantages over the older format, including a small form factor and a rigid case with a slideable write protect catch. The almost-universal use of the 5¼-inch format made it very difficult for any of these new formats to gain any significant market share.
Sony introduced their own small-format 90.0 mm × 94.0 mm disk, similar to the others but somewhat simpler in construction than the AmDisk. The first computer to use this format was Sony's SMC 70 of 1982. Other than Hewlett-Packard's HP-150 of 1983 and Sony's MSX computers that year, this format suffered from a similar fate as the other new formats: the 5¼-inch format simply had too much market share. A variant on the Sony design, introduced in 1982 by a large number of manufacturers was then rapidly adopted. By 1988 the 3½-inch was outselling the 5¼-inch.
By the end of the 1980s, the 5¼-inch disks had been superseded by the 3½-inch disks. Though 5¼-inch drives were still available, as were disks, they faded in popularity as the 1990s began. The main community of users was primarily those who still owned '80s legacy machines (PCs running MS-DOS or home computers) that had no 3½-inch drive; the advent of Windows 95 (not even sold in stores in a 5¼-inch version; a coupon had to be obtained and mailed in) and subsequent phaseout of standalone MS-DOS with version 6.22 forced many of them to upgrade their hardware. On most new computers the 5¼-inch drives were optional equipment. By the mid-1990s the drives had virtually disappeared as the 3½-inch disk became the predominant floppy disk.
The main technological change was the addition of tracking information on the disk surface to allow the read/write heads to be positioned more accurately. Normal disks have no such information, so the drives use the tracks themselves with a feedback loop in order to center themselves. The newer systems generally used marks burned onto the surface of the disk to find the tracks, allowing the track width to be greatly reduced.
Apparently it used 3½-inch standard disks which had servo information embedded on them for use with the Twin Tier Tracking technology.
Insite licenced their technology to a number of companies, who introduced compatible devices as well as even larger-capacity formats. Most popular of these, by far, was the LS-120, mentioned below.
It was upgraded ("LS-240") to 240 MB (240.75 MB). Not only could the drive read and write 1440 kB disks, but the last versions of the drives could write 32 MB onto a normal 1440 kB disk (see note below). Unfortunately, popular opinion held the Super Disk disks to be quite unreliable, though no more so than the Zip drives and SyQuest Technology offerings of the same period and there were also many reported problems moving standard floppies between LS-120 drives and normal floppy drives. This belief, true or otherwise, crippled adoption. The BIOS of many motherboards even to this day supports LS-120 drives as boot options.
After only a short time on the market the product was pulled, as it was discovered there were a number of performance and reliability problems that made the system essentially unusable. Sony then re-engineered the device for a quick re-release, but then extended the delay well into 1998 instead, and increased the capacity to "200 MB" (approximately 210 megabytes) while they were at it. By this point the market was already saturated by the Zip disk, so it never gained much market share.
The 5¼-inch disk had a large circular hole in the center for the spindle of the drive and a small oval aperture in both sides of the plastic to allow the heads of the drive to read and write the data. The magnetic medium could be spun by rotating it from the middle hole. A small notch on the right hand side of the disk would identify whether the disk was read-only or writable, detected by a mechanical switch or photo transistor above it. Another LED/phototransistor pair located near the center of the disk could detect a small hole once per rotation, called the index hole, in the magnetic disk. It was used to detect the start of each track, and whether or not the disk rotated at the correct speed; some operating systems, such as Apple DOS, did not use index sync, and often the drives designed for such systems lacked the index hole sensor. Disks of this type were said to be soft sector disks. Very early 8-inch and 5¼-inch disks also had physical holes for each sector, and were termed hard sector disks. Inside the disk were two layers of fabric designed to reduce friction between the medium and the outer casing, with the medium sandwiched in the middle. The outer casing was usually a one-part sheet, folded double with flaps glued or spot-welded together. A catch was lowered into position in front of the drive to prevent the disk from emerging, as well as to raise or lower the spindle (and, in two-sided drives, the upper read/write head).
The 3½-inch disk is made of two pieces of rigid plastic, with the fabric-medium-fabric sandwich in the middle to remove dust and dirt. The front has only a label and a small aperture for reading and writing data, protected by a spring-loaded metal or plastic cover, which is pushed back on entry into the drive.
The reverse has a similar covered aperture, as well as a hole to allow the spindle to connect into a metal plate glued to the medium. Two holes, bottom left and right, indicate the write-protect status and high-density disk correspondingly, a hole meaning protected or high density, and a covered gap meaning write-enabled or low density. (Incidentally, the write-protect and high-density holes on a 3½-inch disk are spaced exactly as far apart as the holes in punched A4 paper (8 cm), allowing write-protected floppies to be clipped into European ring binders.) A notch top right ensures that the disk is inserted correctly, and an arrow top left indicates the direction of insertion. The drive usually has a button that, when pressed, will spring the disk out at varying degrees of force. Some would barely make it out of the disk drive; others would shoot out at a fairly high speed. In a majority of drives, the ejection force is provided by the spring that holds the cover shut, and therefore the ejection speed is dependent on this spring. In PC-type machines, a floppy disk can be inserted or ejected manually at any time (evoking an error message or even lost data in some cases), as the drive is not continuously monitored for status and so programs can make assumptions that do not match actual status (e.g., disk 123 is still in the drive and has not been altered by any other agency). With Apple Macintosh computers, disk drives are continuously monitored by the OS; a disk inserted is automatically searched for content and one is ejected only when the software agrees the disk should be ejected. This kind of disk drive (starting with the slim "Twiggy" drives of the late Apple "Lisa") does not have an eject button, but uses a motorized mechanism to eject disks; this action is triggered by the OS software (e.g. the user dragged the "drive" icon to the "trash can" icon). Should this not work (as in the case of a power failure or drive malfunction), one can insert a straightened paper clip into a small hole at the drive's front, thereby forcing the disk to eject (similar to that found on CD/DVD drives). Some other computer designs (such as the Commodore Amiga) monitor for a new disk continuously, but still have push-button eject mechanisms.
The 3-inch disk, widely used on Amstrad CPC machines, bears much similarity to the 3½-inch type, with some unique and somewhat curious features. One example is the rectangular-shaped plastic casing, almost taller than a 3½-inch disk, but narrower, and more than twice as thick, almost the size of a standard compact audio cassette. This made the disk look more like a greatly oversized present day memory card or a standard PC card notebook expansion card rather than a floppy disk. Despite the size, the actual 3-inch magnetic-coated disk occupied less than 50% of the space inside the casing, the rest being used by the complex protection and sealing mechanisms implemented on the disks. Such mechanisms were largely responsible for the thickness, length and high costs of the 3-inch disks. On the Amstrad machines the disks were typically flipped over to use both sides, as opposed to being truly double-sided. Double-sided mechanisms were available but rare.
The 8-inch, 5¼-inch and 3-inch formats can be considered almost completely obsolete, although 3½-inch drives and disks are still widely available. As of 2008, 3½-inch drives are still available on some desktop PC systems as an optional extra. Hewlett-Packard has recently dropped supplying floppy drives as standard on business desktops. The majority of ATX and Micro-ATX PC cases are still designed to accommodate at least one 3.5" drive that can be accessed from the front of the PC (although this bay can be used for other devices, such as flash memory readers). As of 2007, HD floppy disks are still quite commonly available in most computer and stationery shops, although selection is usually very limited.
The advent of other portable storage options, such as USB storage devices and recordable or rewritable CDs, and the rise of multi-megapixel digital photography has encouraged the creation and use of files larger than most 3½-inch disks can hold. In addition, the increasing availability of broadband and wireless Internet connections has decreased the utility of removable storage devices overall. The 3½-inch floppy is growing as obsolete as its larger cousin a decade before. However, the 3½-inch floppy has been in continuous use longer than the 5¼-inch floppy.
Floppies are still used for emergency boots in aging systems which may lack support for bootable media such as CD-ROMs and USB devices. They are also still often required for setting up a new PC from the ground up, since even comparatively recent operating systems like Windows XP and Windows Server 2003 rely on third party drivers shipped on floppies: for example, SATA support during installation. Only Windows Vista, using Windows PE, now allows drivers to be loaded from media other than floppies during installation. Floppies are also still often required for BIOS updates, and as maintenance program carriers, since many BIOS and firmware update/restore programs are still designed to be executed from a bootable floppy disk. Floppy drives are also used to access non-critical data that may still be on floppy disks, such as personal data or legacy games and software. As well, office workplaces have often disabled high volume writable media such as optical drivers and USB ports to prevent employees from taking large amounts of data, so the small capacity of the floppy limits the information compromised.
In 1991, Commodore introduced the Amiga CDTV, which used a CD-ROM drive in place of the floppy drive. The majority of AmigaOS was stored on ROM, making it easier to boot from a CD-ROM rather than floppy.
In 1998, Apple introduced the iMac which had no floppy drive. This made USB-connected floppy drives a popular accessory for the early iMacs, since the basic model of iMac at the time had only a CD-ROM drive, giving users no easy access to writable removable media. This transition away from floppies was relatively easy for Apple, since all Macintosh models were able to boot and install their operating system from CD-ROM early on.
In February 2003, Dell, Inc. announced that they would no longer include floppy drives on their Dell Dimension home computers as standard equipment, although they are available as a selectable option for around $20 and can be purchased as an aftermarket OEM add-on anywhere between $5 and $25.
On 29 January 2007 the British computer retail chain PC World issued a statement saying that only 2% of the computers that they sold contained a built-in floppy disk drive and, once present stocks were exhausted, no more floppies would be sold.
The music industry still employs many types of electronic equipment that use floppy disks as a storage medium. Synthesizers, samplers, drum machines, and sequencers continue to use 3½-inch disks. Other storage options, such as CD-R, CD-RW, network connections, and USB storage devices have taken much longer to mature in this industry.
In general, different physical sizes of floppy disks are incompatible by definition, and disks can be loaded only on the correct size of drive. There were some drives available with both 3½-inch and 5¼-inch slots that were popular in the transition period between the sizes.
However, there are many more subtle incompatibilities within each form factor. For example, all but the earliest models of Apple Macintosh computers that have built-in floppy drives included a disk controller that can read, write and format IBM PC-format 3½-inch diskettes. However, few IBM-compatible computers use floppy disk drives that can read or write disks in Apple's variable speed format. For details on this, see the section More on floppy disk formats.
Within the world of IBM-compatible computers, the three densities of 3½-inch floppy disks are partially compatible. Higher density drives are built to read, write and even format lower density media without problems, provided the correct media are used for the density selected. However, if by whatever means a diskette is formatted at the wrong density, the result is a substantial risk of data loss due to magnetic mismatch between oxide and the drive head's writing attempts. Still, a fresh diskette that has been manufactured for high density use can theoretically be formatted as double density, but only if no information has ever been written on the disk using high density mode (for example, HD diskettes that are pre-formatted at the factory are out of the question). The magnetic strength of a high density record is stronger and will "overrule" the weaker lower density, remaining on the diskette and causing problems. However, in practice there are people who use downformatted (ED to HD, HD to DD) or even overformatted (DD to HD) without apparent problems. Doing so always constitutes a data risk, so one should weigh out the benefits (e.g. increased space and/or interoperability) versus the risks (data loss, permanent disk damage).
The holes on the right side of a 3½-inch disk can be altered as to 'fool' some disk drives or operating systems (others such as the Acorn Archimedes simply do not care about the holes) into treating the disk as a higher or lower density one, for backward compatibility or economical reasons . Possible modifications include:
The situation was even more complex with 5¼-inch diskettes. The head gap of an 80 track (1200 kB in the PC world) drive is shorter than that of a 40 track (360 kB in the PC world) drive, but will format, read and write 40 track diskettes with apparent success provided the controller supports double stepping (or the manufacturer fitted a switch to do double stepping in hardware). A blank 40 track disk formatted and written on an 80 track drive can be taken to a 40 track drive without problems, similarly a disk formatted on a 40 track drive can be used on an 80 track drive. But a disk written on a 40 track drive and updated on an 80 track drive becomes permanently unreadable on any 360 kB drive, owing to the incompatibility of the track widths (special, very slow programs could have been used to overcome this problem). There are several other 'bad' scenarios.
Prior to the problems with head and track size, there was a period when just trying to figure out which side of a "single sided" diskette was the right side was a problem. Both Radio Shack and Apple used 360 kB single sided 5¼-inch disks, and both sold disks labeled "single sided" that were certified for use on only one side, even though they in fact were coated in magnetic material on both sides. The irony was that the disks would work on both Radio Shack and Apple machines, yet the Radio Shack TRS-80 Model I computers used one side and the Apple II machines used the other, regardless of whether there was software available which could make sense of the other format.
For quite a while in the 1980s, users could purchase a special tool called a "disk notcher" which would allow them to cut a second "write unprotect" notch in these diskettes and thus use them as "flippies" (either inserted as intended or upside down): both sides could now be written on and thereby the data storage capacity was doubled. Other users made do with a steady hand and a hole punch or scissors. For re-protecting a disk side, one would simply place a piece of opaque tape over the notch or hole in question. These "flippy disk procedures" were followed by owners of practically every home-computer single sided disk drives. Proper disk labels became quite important for such users. Flippies were eventually adopted by some manufacturers, with a few programs being sold in this medium (they were also widely used for software distribution on systems that could be used with both 40 track and 80 track drives but lacked the software to read a 40 track disk in an 80 track drive).
Certain software companies used tracking outside the standard track designations for copy protection. One notable game that used this technique was the popular game Lode Runner, by Brøderbund, which used quarter tracks written on the original disk as a form of copy protection. Because many disk copying programs did not attempt to copy the secret quarter read/write head increment tracks this kind of protection was mostly successful to the average backup program.
However, this is not the most efficient way to use the disk surface, even with available drive electronics. Because the sectors have a constant angular size, the 512 bytes in each sector are packed into a smaller length near the disk's center than nearer the disk's edge. A better technique would be to increase the number of sectors/track toward the outer edge of the disk, from 18 to 30 for instance, thereby keeping constant the amount of physical disk space used for storing each 512 byte sector (see zone bit recording). Apple implemented this solution in the early Macintosh computers by spinning the disk slower when the head was at the edge while keeping the data rate the same, allowing them to store 400 kB per side, amounting to an extra 160 kB on a double-sided disk. This higher capacity came with a serious disadvantage, however: the format required a special drive mechanism and control circuitry not used by other manufacturers, meaning that Mac disks could not be read on any other computers. Apple eventually gave up on the format and used constant angular velocity with HD floppy disks on their later machines; these drives were still unique to Apple as they still supported the older variable-speed format.
Eventually Commodore gave in to disk format standardization, and made its last 5¼-inch drives, the 1570 and 1571, compatible with Modified Frequency Modulation (MFM), to enable the Commodore 128 to work with CP/M disks from several vendors. Equipped with one of these drives, the C128 was able to access both C64 and CP/M disks, as it needed to, as well as MS-DOS disks (using third-party software), which was a crucial feature for some office work.
Commodore also offered its 8-bit machines a 3½-inch 800 kB disk format with its 1581 disk drive, which used only MFM.
The GEOS operating system used a disk format that was largely identical to the Commodore DOS format with a few minor extensions; while generally compatible with standard Commodore disks, certain disk maintenance operations could corrupt the filesystem without proper supervision from the GEOS kernel.
Later DOS versions (3.0 and later 2.5) and DOS systems by third parties (i.e. OSS) accepted(and formatted) disks with up to 960 and 1020 sectors, resulting in 127KB storage capacity per disk side on drives equipped with double-density heads (i.e. not the Atari 810) vs. previous 90KB. That unusual 127K format allowed sectors 1-720 to still be read on a single-density 810 disk drive, and was introduced by Atari with the 1050 drive with the introduction of DOS 3.0 in 1983.
A true 180K double-density Atari floppy format used 128 byte sectors for sectors 1-3, then 256 byte sectors for 4-720. The first three sectors contain code that signals the drive to switch into double-density mode. While this 180K format was developed by Atari for their DOS 2.0D and their (canceled) Atari 815 Floppy Drive, that double-density DOS was never widely released and the format was generally used by third-party DOS products. Under the Atari DOS scheme, sector 360 was the FAT sector map, and sectors 361-367 contained the file listing. The Atari-brand DOS versions and compatible used three bytes per sector for housekeeping and to link-list to the next sector.
Third-party DOS systems added features such as double-sided drives, subdirectories, and drive types such as 1.2Mb and 8". Well-known 3rd party Atari DOS products included SmartDOS (distributed with the Rana disk drive), TopDos, MyDos and SpartaDOS.
The Commodore Amiga computers used an 880 kB format (eleven 512-byte sectors per track) on a 3½-inch floppy. Because the entire track was written at once, inter-sector gaps could be eliminated, saving space. The Amiga floppy controller was much more flexible than the one on the PC: it did not impose arbitrary format restrictions, and foreign formats such as the IBM PC could also be handled (by use of CrossDos, which was included in later versions of Workbench). With the correct filesystem software, an Amiga could theoretically read any arbitrary format on the 3.5-inch floppy, including those recorded at a differential rotation rate. On the PC, however, there is no way to read an Amiga disk without special hardware or a second floppy drive, which is also a crucial reason for an emulator being technically unable to access real Amiga disks inserted in a standard PC floppy disk drive.
Commodore never upgraded the Amiga chip set to support high-density floppies, but sold a custom drive (made by Chinon) that spun at half speed (150 RPM) when a high-density floppy was inserted, enabling the existing floppy controller to be used. This drive was introduced with the launch of the Amiga 3000, although the later Amiga 1200 was only fitted with the standard DD drive. The Amiga HD disks could handle 1760 kB, but using special software programs it could hold even more data. A company named Kolff Computer Supplies also made an external HD floppy drive (KCS Dual HD Drive) available which could handle HD format diskettes on all Amiga computer systems .
Because of storage reasons, the use of emulators and preserving data, many disks were packed into disk-images. Currently popular formats are .ADF (Amiga Disk File), .DMS (DiskMasher) and .IPF (Interchangeable Preservation Format) files. The DiskMasher format is copyright-protected and has problems storing particular sequences of bits due to bugs in the compression algorithm, but was widely used in the pirate and demo scenes. ADF has been around for almost as long as the Amiga itself though it was not initially called by that name. Only with the advent of the Internet and Amiga emulators has it become a popular way of distributing disk images. IPF files were created to allow preservation of commercial games which have copy protection, which is something that ADF and DMS unfortunately cannot do.
For their Electron floppy disk add-on added, Acorn picked 3½-inch disks and developed the Advanced Disc Filing System (ADFS). It used double-density recording and added the ability to treat both sides of the disc as a single drive. This offered three formats: S (small) — 160 KB, 40-track single-sided; M (medium) — 320 KB, 80-track single-sided; and L (large) — 640 KB, 80-track double-sided. ADFS provided hierarchical directory structure, rather than the flat model of DFS. ADFS also stored some metadata about each file, notably a load address, an execution address, owner and public privileges and a "lock" bit. Even on the eight-bit machines, load addresses were stored in 32-bit format.
The ADFS format was later adopted into the BBC line upon release of the BBC Master. The BBC Master Compact marked the move to 3½-inch disks, using the same ADFS formats.
The Acorn Archimedes added D format, which increased the number of objects per directory from 44 to 77, and increased the storage space to 800 KB. The extra space was obtained by using 1024 byte sectors instead of the usual 512 bytes, thus reducing the space needed for inter-sector gaps. As a further enhancement, successive tracks were offset by a sector, giving time for the head to advance to the next track without missing the first sector, thus increasing bulk throughput. The Archimedes used special values in the ADFS load/execute address metadata to store a 12-bit filetype field and a 40-bit timestamp.
RISC OS 2 introduced E format, which retained the same physical layout as D format, but supported file fragmentation and auto-compaction. Post-1991 machines including the A5000 and Risc PC added support for high-density discs with F format, storing 1600 KB. However, the PC combo IO chips used were unable to format discs with sector skew, losing some performance. ADFS and the PC controllers also support extended-density disks as G format, storing 3200 KB, but ED drives were never fitted to production machines.
With RISC OS 3, the Archimedes could also read and write disk formats from other machines, for example the Atari ST and the IBM PC. With third party software it could even read the BBC Micro's original single density 5¼-inch DFS disks. The Amiga's disks could not be read as they used unusual sector gap markers.
The Acorn filesystem design was interesting because all ADFS-based storage devices connected to a module called FileCore which provided almost all the features required to implement an ADFS-compatible filesystem. Because of this modular design, it was easy in RISC OS 3 to add support for so-called image filing systems. These were used to implement completely transparent support for IBM PC format floppy disks, including the slightly different Atari ST format. Computer Concepts released a package that implemented an image filing system to allow access to high density Macintosh format disks.
A small floppy disk was also used in the late 1980s to store video information for still video cameras such as the Sony Mavica (not to be confused with current Digital Mavica models) and the Ion and Xapshot cameras from Canon. It was officially referred to as a Video Floppy (or VF for short).
VF was not a digital data format; each track on the disk stored one video field in the analog interlaced composite video format in either the North American NTSC or European PAL standard. This yielded a capacity of 25 images per disk in frame mode and 50 in field mode.
The same media were used digitally formatted - 720 kB double-sided, double-density - in the Zenith Minisport laptop computer circa 1989. Although the media exhibited nearly identical performance to the 3½-inch disks of the time, they were not successful. This was due in part to the scarcity of other devices using this drive making it impractical for software transfer, and high media cost which was much more than 3½-inch and 5¼-inch disks of the time.
User available data capacity is a function of the particular disk format used which in turn is determined by the FDD controller manufacturer and the settings applied to its controller. The differences between formats can result in user data capacities ranging from 720 KB (.737 MB) or less up to 1760 KB (1.80 MB) or even more on a "standard" 3½-inch HD floppy. The highest capacity techniques require much tighter matching of drive head geometry between drives; this is not always possible and cannot be relied upon. The LS-240 drive supports a (rarely used) 32 MB capacity on standard 3½-inch HD floppies —it is, however, a write-once technique, and cannot be used in a read/write/read mode. All the data must be read off, changed as needed and rewritten to the disk. The format also requires an LS-240 drive to read.
Some special hardware/software tools, such as the CatWeasel floppy disk controller and software, which claim up to 2.23 MB of formatted capacity on a HD floppy. Such formats are not standard, hard to read in other drives and possibly even later with the same drive, and are probably not very reliable. It is probably true that floppy disks can surely hold an extra 10–20% formatted capacity versus their "nominal" values, but at the expense of reliability or hardware complexity.
DSED 3½" FDDs introduced by Toshiba in 1987 and adopted by IBM on the PS/2 in 1994 operate at twice the data rate and have twice the capacity of DSHD 3½" FDDs. The only serious attempt to speed up a 3.5” floppy drive beyond 2X was a 10X floppy drive. X10 accelerated floppy drive. It used a combo of RAM and 4X spindle speed to read a floppy in less than 6 seconds vs. the over 1 min time it normally takes.
3½-inch HD floppy drives typically have a transfer rate of 1000 kilobits/second (minus overhead such as error correction and file handling). (For comparison a 1X CD transfers at 1200 kilobits/second (maximum), and a 1X DVD transfers at approximately 11,000 kilobits/second.) While the floppy's data rate cannot be easily changed, overall performance can be improved by optimizing drive access times, shortening some BIOS introduced delays (especially on the IBM PC and compatible platforms), and by changing the sector:shift parameter of a disk, which is, roughly, the numbers of sectors that are skipped by the drive's head when moving to the next track.
This happens because sectors are not typically written exactly in a sequential manner but are scattered around the disk, which introduces yet another delay. Older machines and controllers may take advantage of these delays to cope with the data flow from the disk without having to actually stop.
Users damaging floppy disks (or their contents) were once a staple of "stupid user" folklore among computer technicians. These stories poked fun at users who stapled floppies to papers, made faxes or photocopies of them when asked to "copy a disk", or stored floppies by holding them with a magnet to a file cabinet. Also, these same users were, conversely, often the victims of technicians' hoaxes. Stories of them being carried on Subway/Underground systems wrapped in tin-foil to protect them from the magnetic fields of the electric power supply were common (for an explanation of why this is plausible, see Faraday cage). The flexible 5¼-inch disk could also (folklorically) be abused by rolling it into a typewriter to type a label, or by removing the disk medium from the plastic enclosure used to store it safely.
On the other hand, the 3½-inch floppy has also been lauded for its mechanical usability by HCI expert Donald Norman:
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.
For more than two decades, the floppy disk was the primary external writable storage device used. Also, in a non-network environment, floppies have been the primary means of transferring data between computers (sometimes jokingly referred to as Sneakernet or Frisbeenet). Floppy disks are also, unlike hard disks, handled and seen; even a novice user can identify a floppy disk. Because of all these factors, the image of the floppy disk has become a metaphor for saving data, and the floppy disk symbol is often seen in programs on buttons and other user interface elements related to saving files.
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