   #copyright

Floppy disk

2007 Schools Wikipedia Selection. Related subjects: Computing hardware and
infrastructure

   Floppy Disk Drive
   A 3.5 inch diskette, removed from its casing.
   Date Invented: 1969
   Invented By:   David Noble
   Connects to:
     * Motherboard via Proprietary Connector

   Disk Types:
     * High Density
     * Double Density
     * Old

   A floppy disk is a data storage device 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 latter initialism not to be confused with
   "fixed disk drive", which is an old IBM term for a hard disk drive.

Background

   Floppy disks, also known as floppies or diskettes (a name chosen in
   order to be similar to the word "cassette"), were ubiquitous in the
   1980s and 1990s, being used on home and personal computer ("PC")
   platforms such as the Apple II, Macintosh, Commodore 64, Amiga, and IBM
   PC to distribute software, transfer data between computers, and create
   small backups. Before the popularization of the hard drive for PCs,
   floppy disks were often used to store a computer's operating system
   (OS), application software, and other data. Many home computers had
   their primary OS kernels stored permanently in on-board ROM chips, but
   stored the disk operating system on 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 were distributed on sets of floppies. Toward the end of the
   1990s, software distribution gradually switched to CD-ROM, and
   higher-density backup formats were introduced (e.g. the Iomega Zip
   disk). With the arrival of mass Internet access, cheap Ethernet and USB
   keys, the floppy was no longer necessary for data transfer either, and
   the floppy disk was essentially superseded. Mass backups were now made
   to high capacity tape drives such as DAT or streamers, or written to
   CDs or DVDs. One financially unsuccessful attempt in the late 1990s to
   continue the floppy was the SuperDisk (LS-120), with a capacity of 120
   MB (actually 120.375 MiB), while the drive was backward compatible with
   standard 3½-inch floppies.

   Nonetheless, manufacturers were reluctant to remove the floppy drive
   from their PCs, for backward compatibility, and because many companies'
   IT departments appreciated a built-in file transfer mechanism that
   always worked and required no device driver to operate properly. Apple
   Computer was the first mass-market computer manufacturer to drop the
   floppy drive from a computer model altogether with the release of their
   iMac model in 1998, and Dell made the floppy drive optional in some
   models starting in 2003. To date, however, these moves have still not
   marked the end of the floppy disk as a mainstream means of data storage
   and exchange.

   External USB-based floppy disk drives are available for computers
   without floppy drives, and they work on any machine that supports USB.

   Floppy disk sizes are almost universally referred to in imperial
   measurements, even in countries where metric is the standard, and even
   when the size is in fact defined in metric (for instance the 3½-inch
   floppy which is actually 9 cm). Formatted capacities are generally set
   in terms of binary kilobytes (as 1 sector is generally 512 bytes).
   However, recent sizes of floppy are often referred to in a strange
   hybrid unit, i.e. a "1.44 megabyte" floppy is 1.44×1000×1024 bytes, not
   1.44×1024×1024 bytes nor 1.44×1000×1000.

   CAPTION: Historical sequence of floppy disk formats, including the last
   format to be generally adopted — the "1.44 MB" 3½-inch HD floppy,
   introduced 1987.

   Floppy disk format Year introduced Formatted
   Storage capacity
   ( binary kilobytes if not stated) Marketed
   capacity¹
   8-inch - IBM 23FD (read-only) 1969 81.664 kilobytes ←
   8-inch - Memorex 650 1972 175.000 kilobytes 1.5 megabits unformatted
   8-inch - SSSD

   IBM 33FD / Shugart 901
   1973 256.256 kilobytes 3.1 megabits unformatted
   8-inch - DSSD

   IBM 43FD / Shugart 850
   1976 512.512 kilobytes 6.2 megabits unformatted
   5¼-inch (35 track) 1976 89.6 110 kB
   8-inch DSDD

   IBM 53FD / Shugart 850
   1977 1200 1.2 MB
   5¼-inch DD 1978 360 360 kB
   3½-inch
   HP single sided 1982 280 264 kB
   3-inch 1982 360 ←
   3½-inch (DD at release) 1984 720 720 kB
   5¼-inch QD 1984 1200 1.2 MB
   3-inch DD 1984 720 ←
   3-inch
   Mitsumi Quick Disk 1985 128 to 256 ←
   2-inch 1985 720 ←
   5¼-inch Perpendicular 1986 100 MiB ←
   3½-inch HD 1987 1440 1.44 MB
   3½-inch ED 1991 2880 2.88 MB
   3½-inch LS-120 1996 120.375 MiB 120 MB
   3½-inch LS-240 1997 240.75 MiB 240 MB
   3½-inch HiFD 1998/99 150/200 MiB 150/200 MB
   Acronyms:  DD = Double Density; QD = Quad Density; HD = High Density ED
   = Extended Density; LS = Laser Servo; HiFD = High capacity Floppy Disk

   SS = Single Sided; DS = Double Sided
   ¹The formatted capacities of floppy disks frequently corresponded only
   vaguely to their capacities as marketed by drive and media companies,
   primarily 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 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:
     * For 8-inch see Table of 8-inch floppy formats IBM 8" formats. Note
       that 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.

History

Origins, the 8-inch disk

   An 8-inch disk drive with a half-inserted floppy disk.
   Enlarge
   An 8-inch disk drive with a half-inserted floppy disk.

   In 1967 IBM gave their San Jose, California storage development centre
   a new task: develop a simple and inexpensive system for loading
   microcode into their System/370 mainframes. The 370s were the first IBM
   machines to use semiconductor memory, and whenever the power was turned
   off the microcode had to be reloaded ( 'magnetic core' memory, used in
   the 370s' predecessors, the System/360 line, did not lose its contents
   when powered down). Normally this task would be left to various tape
   drives which almost all 370 systems included, but tapes were large and
   slow. IBM wanted something faster and more purpose-built that could
   also be used to send out updates to customers for $5.

   David Noble, working under the direction of Alan Shugart, tried a
   number of existing solutions to see if he could develop a new-style
   tape for the purpose, but eventually gave up and started over. The
   result was a read-only, 8-inch (20 cm) floppy they called the "memory
   disk", holding 80 kilobytes. The original versions were simply the disk
   itself, but dirt became a serious problem and they enclosed it in a
   plastic envelope lined with fabric that would pick up the dirt. The new
   device, developed under the code name Minnow, became a standard part of
   the 370 in 1969.

   A Japanese inventor, Yoshiro Nakamatsu (aka Dr. NakaMats), claims he
   independently came up with the floppy disk principle back in 1950, and
   so a sales license had to be acquired by IBM when they started
   manufacturing their floppy disk systems.

   Alan Shugart left IBM, moved to Memorex where his team in 1972 shipped
   the Memorex 650, the first read-write floppy disk drive.

   In 1973 IBM released a new version of the floppy, this time on the 3740
   Data Entry System. The new system used a different recording format
   that stored up to 250¼ kB on the same disks, and was read-write. These
   drives became common, and soon were being used to move smaller amounts
   of data around, almost completely replacing magnetic tapes.

   The IBM standard soft-sectored disk format was designed to hold just as
   much data as one box of punch cards. The disk was divided into 77
   tracks of 26 sectors, each holding 128 bytes. Note that 77×26 = 2002
   sectors, whereas a box of punch cards held 2000 cards.

   When the first microcomputers were being developed in the 1970s, the
   8-inch floppy found a place on them as one of the few "high speed, mass
   storage" devices that were even remotely affordable to the target
   market (individuals and small businesses). The first microcomputer
   operating system, CP/M, originally shipped on 8-inch disks. However,
   the drives were still expensive, typically costing more than the
   computer they were attached to in early days, so most machines of the
   era used cassette tape instead.

   This began to change with the acceptance of the first standard for the
   floppy disk, ECMA-59, authored by Jim O'Reilly of Burroughs, Helmuth
   Hack of BASF and others. O'Reilly set a record for maneuvering this
   document through ECMA's approval process, with the standard
   sub-committee being formed in one meeting of ECMA and approval of a
   draft standard in the next meeting three months later. This standard
   later formed the basis for the ANSI standard too. Standardization
   brought together a variety of competitors to make media to a single
   interchangeable standard, and allowed rapid quality and cost
   improvement.

   Shugart moved on in 1973 to found Shugart Associates. They started
   working on improvements to the existing 8-inch format, eventually
   creating a new 800 kB system. However, profits were hard to find, and
   in 1974 he was forced out of his own company.

   Burroughs Corporation, meanwhile, was developing a high-performance
   dual-sided 8-inch drive at their Glenrothes, Scotland factory. With a
   capacity of 1 MB (MiB), this unit exceeded IBM's drive capacity by 4
   times, and was able to provide enough space to run all the software and
   store data on the new Burrough's B80 data entry system, which
   incidentally had the first VLSI disk controller in the industry. The
   dual-sided 1MB floppy entered production in 1975, but was plagued by an
   industry problem, poor media quality. There were few tools available to
   test media for 'bit-shift' on the inner tracks, which made for high
   error rates, and the result was a substantial investment by Burroughs
   in a media tester designed by Dr Nigel Mackintosh (who later made
   important contributions to the science of Phase Margin Analysis) that
   they then gave to media makers as a quality control tool, leading to a
   vast improvement in yields.

The 5¼-inch minifloppy (5.25-inch floppy)

   A 5¼-inch disk with a partly exposed magnetic medium spun about a
   central hub for reading. The flexible plastic cover contains a cloth
   inner liner to brush dust from the medium. Note the "write-enable slot"
   to the upper right (confusingly also called a "write-protect notch").
   Enlarge
   A 5¼-inch disk with a partly exposed magnetic medium spun about a
   central hub for reading. The flexible plastic cover contains a cloth
   inner liner to brush dust from the medium. Note the "write-enable slot"
   to the upper right (confusingly also called a "write-protect notch").

   In 1975, Burroughs' plant in Glenrothes developed a prototype 5¼-inch
   drive, stimulated both by the need to overcome the larger 8-inch
   floppy's asymmetric expansion properties with changing humidity, and to
   reflect the knowledge that IBM's audio recording products division was
   demonstrating a dictation machine using 5¼-inch disks. In one of the
   industry's historic gaffes, Burroughs corporate management decided it
   would be "too inexpensive" to make enough money, and shelved the
   program.

   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 took
   the napkin back to California, found it to be 5¼-inches (13 cm) wide,
   and developed a new drive of this size storing 98.5 kB later increased
   to 110 kB by adding 5 tracks. This is believed to be the first standard
   computer medium that was not promulgated by IBM.

   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 from most applications,
   and the 5¼-inch hard-sectored disk format eventually disappeared. These
   early drives read only one side of the disk, leading to the popular
   budget approach of cutting a second write-enable slot and index hole
   into the carrier envelope and flipping it over (thus, the " flippy
   disk") to use the other side for additional storage. This method was
   risky because, when flipped, the disk would spin in the opposite
   direction inside its cover, so some of the dirt that had been collected
   by the fabric lining in the previous rotations would be picked up by
   the disk and dragged past the read/write head.
   Floppy disk write protect tabs. These sticky paper tabs are folded over
   the notch in the side of a 5¼-inch disk to prevent the computer from
   writing data to the disk. Later disks, such as the 3½-inch disk, had a
   built-in slideable plastic tab to implement write-protection.
   Enlarge
   Floppy disk write protect tabs. These sticky paper tabs are folded over
   the notch in the side of a 5¼-inch disk to prevent the computer from
   writing data to the disk. Later disks, such as the 3½-inch disk, had a
   built-in slideable plastic tab to implement write-protection.

   Tandon introduced a double-sided drive in 1978, doubling the capacity,
   and a new "double density" format increased it again, to 360 kB.

   For most of the 1970s and 1980s the floppy drive was the primary
   storage device for microcomputers. Since these micros had no hard
   drive, the OS was usually booted from one floppy disk, which was then
   removed and replaced by another one containing the application. Some
   machines using two disk drives (or one dual drive) allowed the user to
   leave the OS disk in place and simply change the application disks as
   needed. In the early 1980s, 96 track-per-inch drives appeared,
   increasing the capacity from 360 to 720 kB. These did not see
   widespread use, as they were not supported by IBM in its PCs. (Another
   oddball format was used by Digital Equipment Corporation's Rainbow-100,
   DECmate-II and Pro-350. It held 400 kB on a single side by using 96
   tracks-per-inch and cramming 10 sectors per track.)
   Front and back of a floppy with a write-protect tab

   Despite the available capacity of the disks, support on the most
   popular operating system of the early 80's— PC-DOS and MS-DOS—lagged
   slightly behind. In fact, the original IBM PC did not include a floppy
   drive at all as standard equipment—you could either buy the optional
   5¼-inch floppy drive or rely upon the cassette port. With version 1.0
   of DOS (1981) only single sided 160 kB floppies were supported. Version
   1.1 the next year saw support expand to double-sided, 320 kB disks.
   Finally in 1983 DOS 2.0 supported 9 sectors per track rather than 8,
   for a total of 360 kB of disk space. Along with this change came
   support for different directories on the disk (now commonly called
   folders), which came in handy when organizing the greater number of
   files possible in this increased space.

   In 1984, along with the IBM PC/AT, the quad density disk appeared,
   which used 96 tracks per inch combined with a higher density magnetic
   media to provide 1200 kiB of storage (formerly referred to as 1.2
   megabytes). Since the usual (very expensive) hard disk held 10–20
   megabytes at the time, this was considered quite spacious.

   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
   running MS-DOS 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
   preeminent floppy disk.

The "Twiggy" disk

   During the development of the Apple Lisa, Apple developed a disk format
   codenamed Twiggy. While basically similar to a standard 5.25in disk,
   the Twiggy disk had an additional set of write windows on the top of
   the disk with the label running down the side. The drive was also
   present in prototypes of the original Apple Macintosh computer, but was
   removed in both the Mac and later versions of the Lisa in favour of the
   3.5in floppy disk from Sony. The drives were notoriously unreliable and
   Apple was criticized for needlessly diverging from industry standards.

New formats, no standard

   Throughout the early 1980s the limitations of the 5¼-inch format were
   starting to become clear. Originally designed to be a smaller and more
   practical 8-inch, 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 copies of the 8-inch physical format, 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.

   Standard 3-inch and 3½-inch disks used the same spin speed and basic
   hardware interface as standard 5¼-inch drives, allowing them to be used
   with existing controllers and formats, although new formats were later
   developed that relied on the higher quality hardware in the new drive
   types (the IBM PC in particular never officially shared a format
   between the two drive types, though it was possible to misidentify the
   drive to the OS if desired).

The 3-inch compact floppy disk

   The CF has a harder casing than a 3½-inch floppy; the metal door is
   opened by a sliding plastic tab on the right side.
   Enlarge
   The CF has a harder casing than a 3½-inch floppy; the metal door is
   opened by a sliding plastic tab on the right side.

   Original concept of the 3-inch hard case floppy disk was developed in
   1973 by Marcell Jánosi, a hungarian inventor of Budapest Radiotechnic
   Company (Budapesti Rádiótechnikai Gyár - BRG). The system was the BRG
   MCD-1, which was patented but later the patent was not extended,
   therefore the protection lost and Amdek released the AmDisk-3
   Micro-Floppy-disk cartridge system in December 1982. Originally
   designed for use with the Apple II Disk II interface card, it has also
   been connected to other computers successfully.

   The drive itself was originally designed in 1973 by BRG (MCD-1), and
   later in the 80's by Hitachi, Matsushita and Maxell. Only Teac outside
   this "network" is known to have produced drives. Similarly, only three
   manufacturers of media ( Maxell, Matsushita and Tatung) are known
   (sometimes also branded Yamaha, Amsoft, Panasonic, Tandy, Godexco and
   Dixons), but "no-name" disks with questionable quality have been seen
   in the wild.

   Amstrad incorporated a 3-inch single-sided drive into their CPC and PCW
   lines, and this format and the drive mechanism was later "inherited" by
   the ZX Spectrum +3 computer after Amstrad bought Sinclair. Later models
   of the PCW featured double-sided, double density drives.

   While all 3-inch media were double-sided in nature, single-sided drive
   owners were able to flip the disk over to use the other side. The sides
   were termed "A" and "B" and were completely independent, but
   single-sided drive units could only access the upper side at one time.

   The disk format itself had no more capacity than the more popular (and
   cheap) 5¼-inch floppies. Each side held 180 kiB for a total of 360 kiB
   per disk, and later 720 kiB for the PCW range. Unlike 5¼-inch or
   3½-inch disks, the 3-inch disks were designed to be reversible and
   sported two independent write-protect switches. It was also more
   reliable thanks to its hard casing (some reviews at the time reported
   driving over them with no problems).

   3-inch drives were also used on a number of exotic and obscure CP/M
   systems such as the Tatung Einstein and occasionally on MSX systems in
   some regions. Other computers to have used this format are the more
   unknown Gavilan Mobile Computer and Matsushita's National Mybrain 3000.
   The Yamaha MDR-1 also used 3-inch drives.

   The main problems with this format was the high price, due to the quite
   elaborate and complex case mechanisms. However, the tip on the weight
   was when Sony in 1984 convinced Apple Computer to use the 3½-inch
   drives in the Macintosh 128K model, effectively making the 3½-inch
   drive a de-facto standard.

Mitsumi's "Quick Disk" 3-inch floppies

   A Smith Corona DataDisk 2.8-inch actually measures about 3 1/32-inch
   square. This disk is one of the few different Mitsumi Quick Disk
   packages, which vary in storage capacity and casing size. The Quick
   Disk uses a 2.8-inch magnetic media, break-off write-protection tabs
   (one for each side), and contains a see-through hole near center
   spindle (probably used for indexing or to ensure spindle clamping).
   Note the label "A" to indicate disk side. The backside has a "B" label.
   Enlarge
   A Smith Corona DataDisk 2.8-inch actually measures about 3 1/32-inch
   square. This disk is one of the few different Mitsumi Quick Disk
   packages, which vary in storage capacity and casing size. The Quick
   Disk uses a 2.8-inch magnetic media, break-off write-protection tabs
   (one for each side), and contains a see-through hole near centre
   spindle (probably used for indexing or to ensure spindle clamping).
   Note the label "A" to indicate disk side. The backside has a "B" label.

   Another 3-inch format was Mitsumi's Quick Disk format. The Quick Disk
   format is referred to in various size references: 2.8-inch,
   3-inch×3-inch and 3-inch×4-inch. Confusing when trying to categorize
   the disk but perhaps not when understood that Mitsumi offered this as
   OEM equipment, expecting their VAR customers to customize the packaging
   for their own particular use. Nintendo packaged the 2.8-inch magnetic
   media in a 3-inch×4-inch housing, while others packaged the same media
   in a 3″×3″ housing. This explains the different numbering labels, while
   here we generically call the Mitsumi Quick Disk a 3-inch format.

   The Quick Disk's most successful use was in Nintendo's Famicom Disk
   System. The FDS package of Mitsumi's Quick Disk used a 3-inch×4-inch
   plastic housing called the "Disk System Card". Most FDS disks did not
   have cover protection to prevent media contamination, but a later
   special series of five games did include a protective shutter.

   Mitsumi's "3-inch" Quick Disk media was also used in a 3-inch×3-inch
   housing for many Smith Corona word processors. The Smith Corona disks
   are confusingly labeled "DataDisk 2.8 inch", presumably referring to
   the size of the media inside the hard plastic case.

   The Quick Disk was also used in several MIDI keyboards and MIDI
   samplers of the mid 1980s. A non-inclusive list includes: the Roland
   S-10 and MT-100 samplers, the Korg SQD8 MIDI sequencer, Akai's 1985
   model MD280 drive for the S-612 MIDI Sampler, Akai's X7000 and X3700,
   the Roland S-220, and the Yamaha MDF1 MIDI disk drive (intended for
   their DX7/21/100/TX7 synthesizers, RX11/21/21L drum machines, and QX1,
   QX21 and QX5 MIDI sequencers).

   As the cost in the 1980s to add 5.25-inch drives was still quite high,
   the Mitsumi Quick Disk was competing as a lower cost alternative
   packaged in several now obscure 8-bit computer systems. Another
   non-inclusive list of Quick Disk versions: QDM-01, in the Casio QD-7
   drive, in a peripheral for the Sharp MZ-700 & MZ-800 system, in the
   DPQ-280 Quickdisk for the Daewoo/Dynadata MSX1 DPC-200, in a Dragon
   machine, in the Crescent Quick Disk 128, 128i and 256 peripherals for
   the ZX Spectrum, and in the Triton Quick Disk peripherial also for the
   ZX Spectrum and ZX Spectrum.

   The World of Spectrum FAQ reveals that the drives did come in different
   sizes: 128 to 256 kB in Cresent's incarnation, and in the Triton
   system, with a density of 4410 bpi, data transmission rate of 101.6
   kb/s, a 2.8-inch double sided disk type and a capacity of up to 20
   sectors per side at 2.5 kB per sector, up to 100 kB per disk. Quick
   Disk as used in the Famicom Disk System holds 64 kB of data per side,
   requiring a manual turn-over to access the second side.

   It is significant to note that the Quick Disk utilizes "a continuous
   linear tracking of the head and thus creates a single spiral track
   along the disk similar to a record groove." This has led some to
   compare it more to a "tape-stream" unit than typically what is thought
   of as a random-access disk drive.

The 3½-inch microfloppy diskette

   The non-ferromagnetic metal sliding door protects the 3½-inch floppy
   disk's recording medium.
   Enlarge
   The non- ferromagnetic metal sliding door protects the 3½-inch floppy
   disk's recording medium.
   Close up macro photograph of the back of a 3½-inch disk
   Enlarge
   Close up macro photograph of the back of a 3½-inch disk
   The basic internal components of a 3½-inch floppy disk:1. Write-protect
   tab2. Hub3. Shutter4. Plastic housing5. Paper ring6. Magnetic disk7.
   Disk sector.
   Enlarge
   The basic internal components of a 3½-inch floppy disk:
   1. Write-protect tab
   2. Hub
   3. Shutter
   4. Plastic housing
   5. Paper ring
   6. Magnetic disk
   7. Disk sector.

   Sony introduced their own small-format 90.0 × 94.0 mm disk, similar to
   the others but somewhat simpler in construction than the AmDisk. The
   first computer to use this format was the HP-150 of 1983, and Sony also
   used them fairly widely on their line of MSX computers. Other than this
   the format suffered from a similar fate as the other new formats; the
   5¼-inch format simply had too much market share. Things changed
   dramatically in 1984 when Apple Computer selected the format for their
   new Macintosh computers. By 1988 the 3½-inch was outselling the
   5¼-inch.

   The 3½-inch disks had, by way of their rigid case's slide-in-place
   metal cover, the significant advantage of being much better protected
   against unintended physical contact with the disk surface than 5¼-inch
   disks when the disk was handled outside the disk drive. When the disk
   was inserted, a part inside the drive moved the metal cover aside,
   giving the drive's read/write heads the necessary access to the
   magnetic recording surfaces. Adding the slide mechanism resulted in a
   slight departure from the previous square outline. The irregular,
   rectangular shape had the additional merit that it made it impossible
   to insert the disk sideways by mistake as had indeed been possible with
   earlier formats.

   The shutter mechanism was not without its problems, however. On old or
   roughly treated disks the shutter could bend away from the disk. This
   made it vulnerable to being ripped off completely (which does not
   damage the disk itself but does leave it much more vulnerable to dust),
   or worse, catching inside a drive and possibly either getting stuck
   inside or damaging the drive. On disks with the cover bending away the
   best option is to rip the cover off (to make sure it does not catch in
   the drive) and then immediately copy the data off it. Most modern
   floppies have a springy plastic cover that does not tend to bend away
   from the disk.

   Like the 5¼-inch, the 3½-inch disk underwent an evolution of its own.
   When Apple introduced the Macintosh in 1984, it used single-sided
   3½-inch disk drives with an advertised capacity of 400 kB. The encoding
   technique used by these drives was known as GCR, or Group Code
   Recording. Somewhat later, PC-compatible machines began using
   single-sided 3½-inch disks with an advertised capacity of 360 kB (the
   same as a single-sided 5¼-inch disk), and a different, incompatible
   recording format called MFM ( Modified Frequency Modulation). GCR and
   MFM drives (and their formatted disks) were incompatible, although the
   physical disks were the same. In 1986, Apple introduced double-sided,
   800 kB disks, still using GCR, and around the same time, 720 kB
   double-sided double-density MFM disks began to appear on
   PC-compatibles.

   A newer "high-density" format, displayed as "HD" on the disks
   themselves and storing 1440 kB of data, was introduced in 1987. These
   HD disks had an extra hole in the case on the opposite side of the
   write-protect notch. IBM used this format on their PS/2 series
   introduced in 1987. Apple started using "HD" in 1988, on the Macintosh
   IIx, and the HD floppy drive soon became universal on virtually all
   Macintosh and PC hardware. Apple's HD drive was capable of reading and
   writing both GCR and MFM formatted disks, and thus made it relatively
   easy to exchange files with PC users. Apple marketed this drive as the
   "SuperDrive." Interestingly, Apple began using the SuperDrive brand
   name again around 2003 to denote their all-formats CD/DVD
   reader/writer.

   Another advance in the oxide coatings allowed for a new
   "extended-density" ("ED") format at 2880 kB introduced on the second
   generation NeXT Computers in 1991, and on IBM PS/2 model 57 also in
   1991, but by the time it was available it was already too small in
   capacity to be a useful advance over the HD format and never became
   widely used. The 3½-inch drives sold more than a decade later still use
   the same 1.44 MB HD format that was standardized in 1989, in ISO
   9529-1,2.

Reported 3.5" DSHD FDD storage capacity

   The unformatted capacity of 3½-inch double sided high density floppy
   disk is 2.0 megabytes; in its most common format it has a capacity of
   1,474,560 bytes or 1.47 MB (simply dividing by 1,000,000). In the
   binary prefix numbering system this is 1.41 MiB.

   Neither of these numbers is generally used, however. The number most
   frequently printed on these floppies is 1.44 MB. This value was
   apparently reached by doubling (in the decimal system) the capacity of
   the prior generation 720 "KB" [actually KiB] double sided double
   density floppy disk and dividing by 1,000, to arrive at 1.44 kiloKibi
   bytes and mis-labeling such as "MB". A person expecting the 1.44 "MB"
   number to be either binary prefix or decimal would always miscalculate
   the number of floppies needed.

Floppy Replacements

   Through the early 1990s a number of attempts were made by various
   companies to introduce newer floppy-like formats based on the
   now-universal 3½-inch physical format. Most of these systems provided
   the ability to read and write standard DD and HD disks, while at the
   same time introducing a much higher-capacity format as well. There were
   a number of times where it was felt that the existing floppy was just
   about to be replaced by one of these newer devices, but a variety of
   problems ensured this never took place. None of these ever reached the
   point where it could be assumed that every current PC would have one,
   and they have now largely been replaced by CD and DVD burners and USB
   flash drives.

   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 centre
   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.

Flextra

   As early as 1988, Brier Technology introduced the Flextra BR 3020,
   which boasted 21.4 MB (marketing, true size was 21,040 kiB, 25 MiB
   unformatted). Later the same year it introduced the BR3225, which
   doubled the capacity. This model could also read standard 3½-inch
   disks.

   Apparently it used 3½-inch standard disks which had servo information
   embedded on them for use with the Twin Tier Tracking technology.

Floptical

   In 1991, Insite Peripherals introduced the " Floptical", which used an
   infra-red LED to position the heads over marks in the disk surface. The
   original drive stored 21 MiB, while also reading and writing standard
   DD and HD floppies. In order to improve data transfer speeds and make
   the high-capacity drive usefully quick as well, the drives were
   attached to the system using a SCSI connector instead of the normal
   floppy controller. This made them appear to the operating system as a
   hard drive instead of a floppy, meaning that most PCs were unable to
   boot from them. This again adversely affected adoption rates.

   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.

Zip drive

   In 1994, Iomega introduced the Zip drive. Not true to the 3½-inch form
   factor, hence not compatible with the standard 1.44 MB floppies (which
   may have actually been a good thing for the drives as it removed a big
   potential source of problems), it became the most popular of the "super
   floppies". It boasted 100 MB, later 250 MB, and then 750 MB of storage
   and came to market at just the right time, with Zip drives gaining in
   popularity for several years. It never reached the same market
   penetration as floppy drives, as only a few new computers were sold
   with Zip drives. Eventually the falling prices of CD-R and CD-RW media
   and flash drives, and notorious hardware failures (the so-called "
   click of death") reduced the popularity of the the Zip drive.

   A major reason for the failure of the Zip Drives is also attributed to
   the higher pricing they carried. However hardware vendors such as
   Hewlett Packard, Dell and Compaq had promoted the same at a very high
   level. Zip drive media was primarily popular for the excellent
   compression ratio and drive speed they carried, but was always
   overshadowed by the price.

LS-120

   Announced in 1995, the " SuperDisk" drive, often seen with the brand
   names Matsushita (Panasonic) and Imation, had an initial capacity of
   120 MB (120.375 MiB) using even higher density "LS-120" disks.

   It was upgraded ("LS-240") to 240 MB (240.75 MiB). 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 again, true or otherwise, crippled adoption.

Sony HiFD

   Sony introduced their own floptical-like system in 1997 as the 150 MiB
   Sony HiFD. Although by this time the LS-120 had already garnered some
   market penetration, industry observers nevertheless confidently
   predicted the HiFD would be the real floppy-killer and finally replace
   floppies in all machines.

   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 MiB while they were at
   it. By this point the market was already saturated by the Zip disk so
   it never gained much market share.

Caleb Technology’s UHD144

   Little is known about this device except that it surfaced early in 1998
   as the it drive, and provided 144 MB of storage while also being
   compatible with the standard 1.44 MB floppies. The drive was slower
   than its competitors but the media was cheaper, running about $8 at
   introduction and $5 soon after.

Structure

   A user inserts the floppy disk, medium opening first, into a 5¼-inch
   floppy disk drive (pictured, an internal model) and moves the lever
   down (by twisting on this model) to close the drive and engage the
   motor and heads with the disk.
   Enlarge
   A user inserts the floppy disk, medium opening first, into a 5¼-inch
   floppy disk drive (pictured, an internal model) and moves the lever
   down (by twisting on this model) to close the drive and engage the
   motor and heads with the disk.

   The 5¼-inch disk had a large circular hole in the centre 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 centre 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 media and
   the outer casing, with the media sandwiched in the middle. The outer
   casing was usually a one-part sheet, folded double with flaps glued or
   spot-melted 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.

   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 cover, which is pushed back on
   entry into the drive.
   The 3½-inch floppy disk drive automatically engages when the user
   inserts a disk, and disengages and ejects with the press of the eject
   button. On older Macintosh hardware, the disk is lowered into the
   carriage and ejected by a motor (similar to a VCR). To eject a disk on
   a Mac running OS X one would traditionally drag the icon of the
   floppy-disk over the Trash until it turns into an eject icon, then
   release.
   Enlarge
   The 3½-inch floppy disk drive automatically engages when the user
   inserts a disk, and disengages and ejects with the press of the eject
   button. On older Macintosh hardware, the disk is lowered into the
   carriage and ejected by a motor (similar to a VCR). To eject a disk on
   a Mac running OS X one would traditionally drag the icon of the
   floppy-disk over the Trash until it turns into an eject icon, then
   release.

   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 media. 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 (i.e., 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 straight-bent paperclip
   into a small hole at the drive's front, thereby forcing the disk to
   eject (similar to that found on CD/DVD drives).

   The 3-inch disk bears much similarity to the 3½-inch type, with some
   unique and somehow 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 PCMCIA 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.

Current situation

   An example of a modern usb floppy disk drive.
   Enlarge
   An example of a modern usb floppy disk drive.

   The 8-inch, 5¼-inch and 3-inch formats can be considered almost
   completely obsolete. 3½-inch drives and disks are still widely
   available. As of 2006 3½-inch drives are still available on many
   desktop PC systems, although it is usually now an optional extra or has
   to be bought and installed separately. HP 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 can be used for other devices than just floppy drives).
   As of 2006, HD floppy disks are still quite commonly available in most
   computer and stationery shops, although selection is usually very
   limited.

   Floppy disks still maintain a stronghold when it comes to emergency
   boots, BIOS updates and as maintenance program carriers, in general, as
   many BIOS and firmware update/restore programs are still designed to be
   executed from a bootable floppy disk, and the legacy support for
   alternate bootable media such as CD-ROMs and USB devices is still
   problematic in some configurations.

   However, 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 have 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
   is decreasing the utility of removable storage devices overall. The
   3½-inch floppy is growing as obsolete as its larger cousin became a
   decade before. However, the 3½-inch floppy has been in continued use
   longer than the 5¼-inch floppy.

   Some manufacturers have stopped offering 3½-inch drives on new
   computers as standard equipment. The Apple Macintosh, which popularized
   the format in 1984, began to move away from it in 1998 with the iMac
   model—possibly prematurely, since the basic model iMac of the time only
   had a CD-ROM drive, giving users no easy access to removable media.
   This made USB-connected floppy drives a popular accessory for the early
   iMacs. 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 addon
   anywhere between $5 and $25.

Compatibility

   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. Consider, for example, the following Apple/IBM 'schism': Apple
   Macintosh computers can read, write and format IBM PC-format 3½-inch
   diskettes, provided suitable software is installed (it is standard on
   MacOS versions after 7.5). However, many IBM-compatible computers use
   floppy disk drives that are unable to read (or write) Apple-format
   disks. For details on this, see the section More on floppy disk
   formats. In addition, older MFS disks used on early system releases are
   incompatible with later HFS drives used on later Mac models.

   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 is 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; see the Floppy trivia section. 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 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"
   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.
   "Sub Battle Simulator" for the Tandy Color Computer 3 was released in a
   flippy disk
   Enlarge
   "Sub Battle Simulator" for the Tandy Colour Computer 3 was released in
   a flippy disk

   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 media (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).

More on floppy disk formats

Using the disk space efficiently

   In general, data is written to floppy disks in a series of sectors,
   angular blocks of the disk, and in tracks, concentric rings at a
   constant radius, e.g. 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 the amount
   of storage on the disk, although these formats may not be able to be
   read on machines with other controllers; e.g. Microsoft applications
   were often distributed on Distribution Media Format (DMF) disks, a hack
   that allowed 1.68 MB (1680 kiB) to be stored on a 3½-inch floppy by
   formatting it with 21 sectors instead of 18, while these disks were
   still properly recognized by a standard controller.) On the IBM PC and
   also on the MSX, Atari ST, Amstrad CPC, and most other microcomputer
   platforms, disks are written using a Constant Angular Velocity
   (CAV)—Constant Sector Capacity format. This means that the disk spins
   at a constant speed, and the sectors on the disk all hold the same
   amount of information on each track regardless of radial location.

   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 centre 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 standard HD floppy drives on their later
   machines.

The Commodore 64/128

   Commodore started its tradition of special disk formats with the
   5¼-inch disk drives accompanying its PET/CBM, VIC-20 and Commodore 64
   home computers, like the 1540 and (better-known) 1541 drives used with
   the latter two machines. The standard Commodore Group Code Recording
   scheme used in 1541 and compatibles employed four different data rates
   depending upon track position (see zone bit recording). Tracks 1 to 17
   had 21 sectors, 18 to 24 had 19, 25 to 30 had 18, and 31 to 35 had 17,
   for a disk capacity of 170 kB (170.75 kiB).

   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.

The Commodore Amiga

   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. They were also famous for the
   KCS Power Cartridge.

   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.

The Acorn Archimedes

   Another machine using a similar "advanced" disk format was the British
   Acorn Archimedes, which could store 800 kB on a 3½-inch DD floppy using
   the ADFS D and E formats. Later Archimedes models and the Risc PC could
   also store 1600 kB on a 3½-inch HD floppy using ADFS's F format. It
   could also read and write disk formats from other machines, for example
   the Atari ST and the IBM PC. It was also capable of reading and writing
   the 640 kB format of earlier versions of ADFS for the BBC model B, B+,
   Master and the Acorn Electron. With third party software it could even
   read the BBC Micro's original single density DFS disks. The Amiga's
   disks could not be read as they used a non-standard sector size and
   unusual sector gap markers.

12-inch floppy disks

   In the late 1970s some IBM mainframes also used a 12-inch (30 cm)
   floppy disk, but little information is currently available about their
   internal format or capacity.

4-inch floppies

   IBM in the mid-80s developed a 4-inch floppy. This program was driven
   by aggressive cost goals, but missed the pulse of the industry. The
   prospective users, both inside and outside IBM, preferred
   standardization to what by release time were small cost reductions, and
   were unwilling to retool packaging, interface chips and applications
   for a proprietary design. The product never appeared in the light of
   day, and IBM wrote off several hundred million dollars of development
   and manufacturing facility.

Auto-loaders

   IBM developed, and several companies copied, an autoloader mechanism
   that could load a stack of floppies one at a time into a drive unit.
   These were very bulky systems, and suffered from media hangups and
   chew-ups more than anyone liked, but they were a partial answer to
   replication and large removable storage needs. The smaller 5¼- and
   3½-inch floppy made this a much easier technology to perfect.

Floppy mass storage

   A number of companies, including IBM and Burroughs, experimented with
   using large numbers of unenclosed disks to create massive amounts of
   storage. The Burroughs system used a stack of 256 12-inch disks,
   spinning at high speed. The disk to be accessed was selected by using
   air jets to part the stack, and then a pair of heads flew over the
   surface as in any standard hard disk drive. This approach in some ways
   anticipated the Bernoulli disk technology implemented in the Iomega
   Bernoulli Box, but head crashes or air failures were spectacularly
   messy. The program did not reach production.

2-inch floppy disks

   2-inch Video Floppy Disk from Canon.
   Enlarge
   2-inch Video Floppy Disk from Canon.

   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 was 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, it was not successful.

Ultimate capacity, speed

   It is not easy to provide an answer for data capacity, as there are
   many factors involved, starting with the particular disk format used.
   The differences between formats and encoding methods can result in data
   capacities ranging from 720 kB or less up to 1.72 megabytes (MB) or
   even more on a standard 3½-inch high-density floppy, just from using
   special floppy disk software, such as the fdformat utility, which
   enables "standard" 3½-inch HD floppy drives to format HD disks at 1.62,
   1.68 or 1.72 MB, though reading them back on another machine is another
   story. These 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.

   Sometimes, however, manufacturers provide an "unformatted capacity"
   figure, which is roughly 2.0 MB for a standard 3½-inch HD floppy, and
   should imply that data density cannot (or should not) exceed a certain
   amount. There are, however, 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.

   3½-inch HD floppy drives typically have a transfer rate of 500 kilo
   baud. While this 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 it.

   By changing this parameter, the actual sector sequence may become more
   adequate for the machine's speed. For example, an IBM format 1440 kB
   disk formatted with a sector:shift ratio of 3:2 has a sequential
   reading time (for reading all of the disk in one go) of just 1 minute,
   versus 1 minute and 20 seconds or more of a "normally" formatted disk.
   It is interesting to note that the "specially" formatted disk is
   very—if not completely—compatible with all standard controllers and
   BIOS, and generally requires no extra software drivers, as the BIOS
   generally "adapts" well to this slightly modified format.

Usability

   One of the chief usability problems of the floppy disk is its
   vulnerability. Even inside a closed plastic housing, the disk medium is
   still highly sensitive to dust, condensation and temperature extremes.
   As with any magnetic storage, it is also vulnerable to magnetic fields.
   Blank floppies have usually been distributed with an extensive set of
   warnings, cautioning the user not to expose it to conditions which can
   endanger it.

   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. 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.

The floppy as a metaphor

   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 (although this may change as
   they become less common). 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.

Floppy trivia

     * In some places, especially South Africa and Zimbabwe, 3½-inch
       floppy disks have commonly been called stiffies or stiffy disks,
       because of their "stiff" (rigid) cases, which are contrasted with
       the flexible "floppy" cases of 5¼-inch floppies. In Finnish, the
       term is korppu (rusk, crumpet, biscuit) due to its rigidity
       compared to 5¼-inch lerppu (floppy).
     * Even if such a format was hardly officially supported on any
       system, it is possible to "force" a 3½-inch floppy disk drive to be
       recognized by the system as a 5¼-inch 360 kB or 1200 kB one (on PCs
       and compatibles, this can be done by simply changing the CMOS BIOS
       settings) and thus format and read non-standard disk formats, such
       as a double sided 360 kB 3½-inch disk. Possible applications
       include data exchange with obsolete CP/M systems, for example with
       an Amstrad CPC.
     * If the cable for a 3½-inch floppy disk drive is incorrectly
       connected to the floppy drive controller with a 180°-twist, the
       floppy drive LED will remain on.
     * In the early days, manufacturers of "single sided" floppy disks
       would advise consumers that they "certified" only one side (hence
       the name single-sided), and if the user wanted to use the other
       side of the diskette, they should buy the more expensive
       "double-sided" variety of floppy disks. Consumers quickly found
       that since some single-head floppy drives had their read/write
       heads on the bottom and some had them on the top, that the
       manufacturers ended up certifying both sides anyway, thereby making
       the single-sided diskettes usable on both sides regardless.
     * On the disk drives of the old Atari 8-bit family of computers, the
       drive activity indicator LEDs were actually part of the power
       circuit. If they burned out, the drive would stop working.
     * Atari developed a 3.5" 360k drive for their 8-bit line, the XF351.
       However the Tramiel's in their marketing wisdom chose to avoid
       confusion with their ST line and it was never released, much to the
       chagrin of many 8-bit users to this day.
     * On the disk drives of the Atari ST, Commodore computers, and
       possibly others as well, the drive activity indicator LEDs were
       software controllable. This was put to use in some games, for
       example in the ST version of Lemmings, where the LED would blink as
       the three last building bricks were used by the bridge builder
       lemming. In the absence of audio cues (e.g., when not listening to
       the in-game sound), this was critical to prevent the builder
       lemming from falling down after completing a bridge.
     * The " Elk Cloner" virus of 1982 exploited a security hole in the
       booting from a floppy disk to contaminate other floppy disks
       inserted into the computer since bootup.
     * Certain software companies used tracking outside the standard track
       designations for copy protection. One notable game that used this
       technique was the popular game by Brøderbund Lode Runner 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.
       Because disk drives were unable to reliably write quarter track
       increments this provided a somewhat reliable protection in general.
     * It was possible with the Commodore 1541 and 1571 disk drives to
       vibrate the head carriage against a "Track-0" head stop at varying
       frequencies to create simple musical melodies.
     * There is an urban myth that it is safe to view a solar eclipse
       through the film of a floppy removed from its case. Despite some
       anecdotal support, this is in fact dangerous and can lead to
       retinal damage and even blindness. Moreover, it produces poor image
       quality compared to filters designed for this purpose.
     * 3½-inch disks were frequently advertised in Europe as "88,9 mm
       disks"—an accurate, if overly precise, conversion, but the disks
       are actually 90 mm wide.
     * 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. Popular modifications include:
          + Drilling or cutting an extra hole into the right-lower side of
            a 3½-inch DD disk (symmetrical to the write-protect hole) in
            order to format the DD disk into a HD one. This was a popular
            practice during the early 1990s, as most people switched to HD
            from DD during those days and some of them "converted" some or
            all of their DD disks into HD ones, for gaining an extra
            "free" 720 kiB of disk space. The success ratio was very high,
            especially as late DD disks used the same materials as HD
            ones, so they had no problem supporting the higher density. In
            general, only very old (made before 1989) DD disks were likely
            to exhibit faults and read/write errors.
          + Vice versa, taping the right hole on a HD 3½-inch disk enables
            it to be 'downgraded' to DD format. This may sound
            counterproductive at first, but there are practical scenarios,
            e.g. compatibility issues with older computers, drives or
            devices that use DD floppies, like some electronic keyboard
            instruments and samplers where a 'downgraded' disk can be
            useful, as factory-made DD disks have become hard to find
            after the mid-1990s. See the section "Compatibility" above. It
            is important to note that due to read/write voltage
            differences in the heads of DD vs. HD disks, writing to an HD
            floppy with a DD drive (or an HD drive in DD mode) is widely
            considered to be a highly unreliable method of storing data.
               o Note: By default, many older HD drives will recognize ED
                 disks as DD ones, since they lack the HD-specific holes
                 and the drives lack the sensors to detect the ED-specific
                 hole. Most DD drives will also handle ED (and some even
                 HD) disks as DD ones.
          + Similarly, drilling an HD-like hole (under the ED one) into an
            ED (2880 kiB) disk for 'downgrading' it to HD (1440 kiB)
            format. This can turn useful if there are many unusable ED
            disks due to the lack of a specific ED drive, which can now be
            used as normal HD disks. In general, they work pretty well.
          + Finally, it is possible to "upgrade" a HD disk into an ED one
            by drilling an ED-positioned hole above the HD one, although
            the considerations made for DD vs HD disk material are
            probably not valid for HD vs ED, and such "upgraded" disks are
            probably not reliable.
          + Double disk 'upgrades' or 'downgrades' are possible by
            drilling ED holes into DD disks or taping ED disks.
     * New Order's classic dance track " Blue Monday" owes some of its
       popularity to the 12-inch version of the single initially being
       shipped in a sleeve designed to resemble a 5¼-inch floppy. Legend
       has it that it was so expensive to produce the sleeve that Factory
       Records lost money despite the single's runaway success. Fatboy
       Slim's 1995 album Better Living Through Chemistry features a
       3½-inch floppy with the track names on its label as the main album
       art in homage to Blue Monday.
     * In Marvel's Transformers comics continuity, Optimus Prime's
       personality was downloaded onto a floppy disk after his death.

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