The Online Encyclopedia and Dictionary






Floppy disk

A floppy disk is a data storage device that is composed of a circular piece of thin, flexible (i.e. "floppy") magnetic storage medium encased in a square or rectangular plastic wallet. Floppy disks are read and written by a floppy disk drive or FDD, the latter acronym not to be confused with "fixed disk drive", which is an old IBM term for a hard disk drive.

Historical sequence of floppy disk formats, including the last format to be ubiquitously adopted (3½-inch HD).
DD = Double Density; QD = Quad Density; HD = High Density; ED = Extra High Density.
Floppy disk format Year introduced Storage capacity
8-inch 1971 80 KB
8-inch 1973 256 KB
8-inch 1974 800 KB
8-inch dual-sided 1975 1,000 KB
5¼-inch 1976 110 KB
5¼-inch DD 1978 360 KB
5¼-inch QD 1984 1,200 KB
3-inch 1984? 360 KB
3-inch (DD) 1984? 720 KB
3½-inch DD 1984 720 KB
2-inch 1985? 720?KB
3½-inch HD 1987 1,440 KB
3½-inch ED 1991 2,880 KB


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and USB "keydrives", the floppy was no longer necessary for data transfer either, and the floppy disk was essentially superseded.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 unsuccessful (in the marketplace) attempt in the late 1990s to continue the floppy was the SuperDisk (LS120) with a capacity of 120 MB 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, though, 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 disks are almost universally referred to in imperial measurements, even in countries where metric is the standard. [Note: Throughout this article, the "K" is used to indicate the "binary kilo" (1,024).]


Origins, the 8-inch disk

In 1967 IBM gave their San Jose, California storage development center 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 (KB). 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 became a standard part of the 370 in 1971.

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.

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 256 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.

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 International-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.

By this time Alan Shugart had left IBM, moved to Memorex for a brief time, and then again 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 was meanwhile developing a high-performance dual-sided 8-inch drive at their Glenrothes, Scotland, factory. With a capacity of 1 MB, 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 design that they then gave to media makers as a quality control tool, leading to a vast improvement in yields.

The 5¼-inch minifloppy

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.
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.

In 1975, Burroughs' plant in Glenrothes developed a prototype 5.25-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 5.25" 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 one of Shugart [Assoc.]'s employees, Jim Adkisson, was 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 110 KB.

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 Assoc. was producing 4,000 drives a day. By 1978 there were more than 10 manufacturers producing 5¼-inch floppy drives, and the format quickly displaced the 8-inch from most applications. 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.

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 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. 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 1200KB of storage (normally and misleadingly reffered 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. 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 pre-eminent floppy disk.

The 3-inch compact floppy disk

A now unused semi-proprietary format, the 3-inch Compact Floppy was a format used mainly on the Amstrad CPC, PCW and ZX Spectrum computers while these machines were still supported, as well as on a number of exotic and obscure CP/M systems such as the Einstein or Osborne computers and occasionally on MSX systems in some regions. The disk format itself was not more capient than the more popular (and cheap) 5¼" floppies, but was more reliable thanks to its hard casing (some reviews at the time reported driving over them with no problems).

Their main problems were their high prices, due to their quite elaborate and complex case mechanisms and low nominal capacities, as well as their being bound to using specifically designed drives, which were very hard to repair or replace.

Eventually, the format died out along with the computer systems that used it.

The 3½-inch micro floppy diskette

The non- metal sliding door protects the 3½-inch floppy disk's recording medium.
The non-ferromagnetic metal sliding door protects the 3½-inch floppy disk's recording medium.

Throughout the early 1980s the limitations of the 5¼-inch format were starting to become clear as machines grew in power. 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. Amstrad incorporated a 3-inch 180 KB single-sided disk 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 Research. Later models of the PCW featured double-sided, quad density drives while all 3-inch media were double-sided in nature with single-sided drive owners able to flip the disk over to use the other side. Media in this format remained expensive and it never caught on with only three manufacturers producing media - Amstrad, Tatung and Maxell.

Things changed dramatically in 1984 when Apple Computer selected the Sony 90.0 × 94.0 mm format for their Macintosh computers, thereby forcing it to become the standard format in the United States. (This is yet another example of a "silent" change from metric to imperial units; this product was advertised and became popularly known as the 3½-inch disk, emphasizing the fact that it was smaller than the existing 5¼-inch.) The first computer to use this format was the HP-150 of 1983. By 1989 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 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 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.)

Like the 5¼-inch, the 3½-inch disk underwent an evolution of its own. They were originally offered in a 360 KB single-sided and 720 KB double-sided double-density format (the same as then-current 5¼-inch disks). A newer "high-density" format, displayed as "HD" on the disks themselves and storing 1440 KB of data, was introduced in the mid-80s. IBM used it on their PS/2 series introduced in 1987. Apple started using "HD" in 1988, on the Macintosh IIx. Another advance in the oxide coatings allowed for a new "extended-density" ("ED") format at 2880 KB (normally and misleadingly reffered to as 2.88 MB) introduced on the second generation NeXT Computers in 1991, but by the time it was available it was already too small to be a useful advance over 1440 KB, and never became widely used. The 3½-inch drives sold more than a decade later still used the same format that was standardized in 1989, in ISO 9529-1,2.

Not long after the 2880 KB format was declared DOA by the market, it became obvious that users had a requirement to move around ever increasing amounts of data. A number of products surfaced, but only a few maintained any level of backward compatibility with 3½-inch disks. Insite Peripherals' "Floptical" was the first off the blocks, offering 20, 40 and ultimately 80 MB devices that would still read and write 1440KB disks. However, the drives did not connect to a normal floppy disk controller, meaning that many older PCs were unable to boot up from a disk in a Floptical drive. This again adversely affected adoption rates.

Announced in 1995, the "Super Disk" drive, often seen with the brand names Matsushita (Panasonic) and Imation, had an initial capacity of 120 MB. It was subsequently upgraded to 240 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. This again, true or otherwise, crippled adoption.

Thus 3½-inch disks are still widely available. As of 2004 3½-inch drives are still common equipment on most new PCs. On others, they are either optional equipment, or can be purchased as after-market equipment. However, with the advent of other portable storage options, such as Zip disks, USB storage devices, and (re)writable CD's the 3½-inch disk is becoming increasingly obsolete. 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.

The formatted capacity of 3½-inch high-density floppies was originally 1440 kibibytes (KiB), or 1,474,560 bytes. This is equivalent to 1.41 MiB (1.47 MB decimal). However, their capacity is usually reported as 1.44 MB by diskette manufacturers.

In some places, especially South Africa, 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.

Even if such a format was hardly officially supported on any system, it is possible to "force" a 3½ floppy disk drive to be recognized by the system as a 5¼ 360KB or 1200KB 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 360KB 3½ disk. Possible applications include data exchange with obsolete CP/M systems, for example with an Amstrad CPC.


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.
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 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 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. 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 a button, or by motor on the .
The 3½-inch floppy disk drive automatically engages when the user inserts a disk, and disengages and ejects with the press of a button, or by motor on the Apple Macintosh.

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 don't match actual status (ie, 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 a lot of 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 per cent 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.


In general, different physical sizes of floppy disks are incompatible by definition, and disks can only be loaded 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. 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".

Within the world of IBM-compatible computers, the three densities of 3½-inch floppy disks are partly 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.

The situation was even more complex with 5¼-inch diskettes. The head gap of a 1200 KB drive is shorter than that of a 360 KB drive, but will format, read and write 360 KB diskettes with apparent success. A blank 360 KB disk formatted and written on a 1200 KB drive can be taken to a 360 KB drive without problems, similarly a disk formatted on a 360 KB drive can be used on a 1200 KB drive. But a disk written on a 360 KB drive and updated on a 1200KB drive becomes permanently unreadable on any 360 KB drive, owing to the incompatibility of the track widths. 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.

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. For re-protecting a disk side, one would simply place a piece of opaque tape over the notch/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.

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 'Microsoft distribution format' disks, a hack that allowed 1.68 MB 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 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 80 KB on a double-sided disk. This higher capacity came with a serious disadvantage, though; 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 128

The Commodore 128 used a special 3½-inch 800 KB disk format with its 1581 disk drive (which was compatible with all 8-bit CBM serial-bus based machines). Commodore actually started its tradition of special disk formats with the 5¼-inch disk drives accompanying its PET/CBM, VIC-20 and C64 home computers, like the 1540 and (better-known) 1541 drives used with the latter two machines. These disk drives used Commodore's in-house developed Group Code Recording, based on up to four different data rates according to the track position.

Eventually, however, Commodore had to give 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 C128 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. A typical usage would be to copy MS-DOS text files off PCs at one's workplace and take the files home to edit on a C128.

The Commodore Amiga

The Commodore Amiga computers used other kinds of floppy disk optimizations for extra storage, mainly the elimination of gaps between sectors (the entire track was written at once). This allowed 11 (512-byte) sectors per track instead of 9; a total of 880 KB on a DD floppy, and 1.76 MB on HD. Further tricks used by third-party developers, such as shrinking the end-of-track gap and removal of the generally unused "sector label" headers, allowed for 12 sectors per track and thus 960 KB on a standard DD floppy or 1.87 MB on HD. The flexible floppy controller did not impose arbitrary format restrictions, and foreign formats such as the IBM PC could also be handled.

The Amiga OS constantly monitors changes in the floppy drive state. This allows the Amiga to immediately recognize when a disk has been inserted or removed. This removes the need for the user to respond by clicking a system request.

The Acorn Archimedes

Another machine using a similar "advanced" disk format was the British Acorn Archimedes, which could store 1.6 MB on a 3½-inch HD floppy. It could also read and write disk formats from other machines, for example the Atari ST and the IBM PC. 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-80's 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.


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 5.25 and 3.5-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 prefaced the Bernoulli disk from Iomega, but head crashes or air failures were spectacularly messy. Unfortunately, the program did not reach production.

2-inch floppy 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 Canon (company) Ion.

This was not a digital data format; each track on the disk stored one video field from the interlaced composite video format. This yielded a capacity of 25 images per disk in frame mode and 50 in field mode.

The same media was used digitally formatted - 720K double-sided, double-density - in the Zenith Minisport laptop computer circa 1989. Although the media exhibited nearly identical performance to the 3.5" 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 720KB 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 can't be relied upon. The LS-240 drive supports a (rarely used) 32MB capacity on standard 3½" 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. And it 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 can't (or shouldn't) 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's 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 kilobaud. 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 aren't 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's 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.


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 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 (here quoted from his book The Design of Everyday Things , Chapter 1):

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 now, the floppy disk has been 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 disk/drive trivia

  • On the disk drives of the Atari ST, Commodore computers, and possibly others as well, the drive activity indicator LEDs are 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.
  • It was possible to manually force the movement of the drive head carriage in the Commodore 1541 and 1571 disk drives by the use of special commands. This was often used in demo programs to vibrate the head carriage against a "Track-0" head stop at varying frequencies to create simple musical melodies (e.g., Amazing Grace).
  • The standard Commodore GCR scheme used in 1541 and compatibles employed the use of differing sectors depending upon track position: Tracks 1 to 17 had 21 sectors, 18 to 24 had 19, 25 to 30 had 18, and 31 to 35 had 17. This allowed the 1541 to maximize available space to store 167k rather than, and contrary to common folklore, using a variable spindle speed. (The drive maintained 300rpm at all positions.)
  • 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 retina damage and even blindness ([1], [2]). Moreover, it produces poor image quality compared to filters designed for this purpose.

See also

  • RaWrite2 (a floppy disk image file writer/creator)
  • Zip drive (a newer, larger and proprietary format for removeable storage)
  • On Unix or Unix-like systems the dd program can be used to write an image to a floppy.


External links

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