Floppy disk

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A 3½-inch diskette's "floppy" magnetic material, removed from its housing

A floppy disk, also called a diskette, is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. Floppy disks are read and written by a floppy disk drive (FDD).


By 2010, computer motherboards were rarely manufactured with floppy drive support; 3½-inch floppy disks can be used with an external USB floppy disk drive, but USB drives for 5¼-inch, 8-inch and non-standard diskettes are rare or non-existent, and those formats must usually be handled by old equipment.




The earliest floppy disks, developed in the late 1960s, were 8 inches (200 mm) in diameter;[1] they became commercially available in 1971.[2] These disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation.[3] The phrase "floppy disk" appeared in print as early as 1970,[4] and although in 1973 IBM announced its first media as "Type 1 Diskette" the industry continued to use the terms "floppy disk" or "floppy".

In 1976, Shugart Associates introduced the first 5¼-inch FDD. By 1978 there were more than 10 manufacturers producing such FDDs. There were competing floppy disk formats, with hard and soft sector versions and encoding schemes such as FM, MFM and GCR. The 5¼-inch format displaced the 8-inch one for most applications, and the hard-sectored disk format disappeared. In 1984, IBM introduced the 1.2 MB dual-sided floppy disk along with its AT model. IBM started using the 720 KB double-density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and the 1.44 MB high-density version with the PS/2 line in 1987. These disk drives could be added to older PC models. In 1988 IBM introduced a drive for 2.88 MB "DSED" diskettes in its top-of-the-line PS/2 models, but this was a commercial failure.


By the end of the 1980s, the 5¼-inch disks had been superseded by the 3½-inch disks. By the mid-1990s, the 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. The advantages of the 3½-inch disk were its smaller size and its plastic case, which provided better protection from dirt and other environmental risks, while the 5¼-inch disk was available cheaper per piece throughout its history, usually with a price in the range of 1/3 to 2/3 of a 3½-inch disk.[citation needed]



Floppy disks became ubiquitous in the 1980s and 1990s in their use with personal computers to distribute software, transfer data, and create backups. Before hard disks became affordable, floppy disks were often used to store a computer's operating system (OS). Most home computers had a primary OS and BASIC stored as ROM, with the option of loading a more advanced disk operating system from a floppy disk. By the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were an estimated five billion floppy disks in use.[7] Then, distribution of larger packages was gradually replaced by CD-ROM and online distribution (for smaller programs). An attempt to continue the floppy disk was the SuperDisk in the late 1990s, with a capacity of 120 MB[8] and backward-compatible with standard 3½-inch floppies; a format war briefly occurred between SuperDisk and other high-density removable disk products, although ultimately flash memory, recordable CDs/DVDs, and online storage would render the matter irrelevant. External USB-based floppy disk drives are still available; many modern systems provide firmware support for booting from such drives.



Apple introduced the iMac in 1998 with a CD-ROM drive but no floppy drive; this made USB-connected floppy drives popular accessories, as the iMac came without any writable removable media device. This transition from standard floppies was relatively easy for Apple, since all Macintosh models originally designed to use a CD-ROM drive could boot and install their operating system from CD-ROM early on.


Use in the early 21st century[edit]

A floppy hardware emulator, same size as a 3½ drive, provides a USB interface to the user

Nonetheless, as of 2002 most manufacturers still provided floppy disk drives as standard equipment to meet user demand for file-transfer and an emergency boot device as well as the general secure feeling of having the familiar device.[9] Subsequently, enabled by the widespread support for USB flash drives and BIOS boot, manufacturers and retailers progressively reduced the availability of floppy disk drives as standard equipment. In February 2003, Dell announced that floppy drives would no longer be pre-installed on Dell Dimension home computers, although they were still available as a selectable option and purchasable as an aftermarket OEM add-on.[10] On 29 January 2007, PC World stated that only 2% of the computers they sold contained built-in floppy disk drives; once present stocks were exhausted, no more standard floppies would be sold.[11] In 2009, Hewlett-Packard stopped supplying standard floppy drives on business desktops.[citation needed]


Corporate computer environments may still make use of floppy disks for older machines that do not support the current company networks and in the case of laptops where Wi-Fi is not considered secure.[citation needed] The floppy disk provides for a controlled means of file transfer by permitting only a few files to be transmitted. This is as USB ports on enterprise computer terminals/workstations are often disabled in order to prevent employees from using a flash memory drive to take large amounts of data for unauthorized use. In addition, the loss of a floppy disk has fewer consequences than the loss of a flash drive.















The spindle motor from a 3½‑inch unit
A read-write head from a 3½‑inch unit


How the read-write head is applied on the floppy

A spindle motor in the drive rotates the magnetic medium at a certain speed, while a stepper motor-operated mechanism moves the magnetic read/write head(s) along the surface of the disk. Both read and write operations require the media to be rotating and the head to contact the disk media, an action accomplished by a "disk load" solenoid.[15] To write data, current is sent through a coil in the head as the media rotates. The head's magnetic field aligns the magnetic particles directly below the head on the media. When the current is reversed the particles align in the opposite direction encoding the data digitally. To read data, the magnetic particles in the media induce a tiny voltage in the head coil as they pass under it. This small signal is amplified and sent to the floppy disk controller, which converts the streams of pulses from the media into data, checks it for errors, and sends it to the host computer system.





8-inch floppy disk[edit]

8-inch floppy disk

The first floppy disk was 8 inches in diameter, was protected by a flexible plastic jacket and was a read-only device used by IBM as a way of loading microcode.[16] Read/Write floppy disks and their drives became available in 1972 but it was IBM's 1973 introduction of the 3740 data entry system[17] that began the establishment of floppy disks, called by IBM the "Diskette 1," as an industry standard for information interchange. Early microcomputers used for engineering, business, or word processing often used one or more 8-inch disk drives for removable storage; the CP/M operating system was developed for microcomputers with 8-inch drives.

The family of 8-inch disks and drives increased over time and later versions could store up to 1.2 MB;[18] many microcomputer applications did not need that much capacity on one disk, so a smaller size disk with lower-cost media and drives was feasible. The 5¼-inch inch drive succeeded the 8-inch size in many applications, and developed to about the same storage capacity as the original 8-inch size, using higher-density media and recording techniques.

5¼-inch floppy disk[edit]



Single sided disks were coated on both sides, despite the availability of more expensive double sided disks. The reason usually given for the higher cost was that double sided disks were certified error-free on both sides of the media. Architectural differences among computer platforms negated this claim, however, with RadioShack TRS-80 Model I computers using one side and the Apple II machines the other. Double-sided disks could be used in drives for single-sided disks, one side at a time, by turning them over (flippy disks); more expensive dual-head drives which could read both sides without turning over were later produced, and eventually became used universally.

3½-inch floppy disk[edit]

Internal parts of a 3½‑inch floppy disk.
1) A hole that indicates a high-capacity disk.
2) The hub that engages with the drive motor.
4) The plastic housing.
6) The magnetic coated plastic disk.
A 3½-inch floppy disk drive.


The first Macintosh computers used single-sided 3½-inch inch floppy disks, but with 400 KB formatted capacity. These were followed in 1986 by double-sided 800 KB floppies. The higher capacity was achieved at the same recording density by varying the disk rotation speed with arm position so that the linear speed of the head was closer to constant. Later Macs could also read and write 1.44 MB HD disks in PC format with fixed rotation speed.

All 3½-inch disks have a rectangular hole in one corner which, if obstructed, write-enabled the disk. The HD 1.44 MB disks have a second, unobstructed hole in the opposite corner which identifies them as being of that capacity.

In IBM-compatible PCs, the three densities of 3½-inch floppy disks are backwards-compatible: higher density drives can read, write and format lower density media. It is physically possible to format a disk at the wrong density, although the resulting disk will not work properly. Fresh disks manufactured as high density can theoretically be formatted at double density only if no information has been written on the disk in high density, or the disk has been thoroughly demagnetized with a bulk eraser, as the magnetic strength of a high density record is stronger and overrides lower density, remaining on the disk and causing problems.

Writing at different densities than disks were intended for, sometimes by altering or drilling holes, was possible but deprecated. The holes on the right side of a 3½‑inch disk can be altered as to make some disk drives and operating systems treat the disk as one of higher or lower density, for bidirectional compatibility or economical reasons.[clarification needed][20][21] Some computers, such as the PS/2 and Acorn Archimedes, ignored these holes altogether.[22]


Other sizes[edit]

Main article: Floppy disk variants

Other smaller floppy size were proposed, especially for portable or pocket-sized devices that needed a smaller storage device. 3-inch disks similar in construction to 3½-inch were manufactured and used for a time, particularly by Amstrad computers and word processors. A 2-inch nominal size was introduced for compact pocket computers and was used with some electronic musical instrument controllers. Neither of these sizes became popular in IBM PC compatible computers.

Sizes, performance and capacity[edit]

Floppy disk size is often referred to in inches, even in countries using metric and though the size is defined in metric. The ANSI specification of 3½-inch disks is entitled in part "90 mm (3.5 in)" though 90 mm is closer to 3.54 inches.[23] Formatted capacities are generally set in terms of kilobytes and megabytes.

Historical sequence of floppy disk formats
Disk format Year introduced Formatted storage capacity Marketed capacity
8-inch: IBM 23FD (read-only) 1971 79.75 kB[24] not marketed commercially
8-inch: Memorex 650 1972 175 kB 1.5 megabit unformatted[25]
8-inch: SSSD

IBM 33FD/Shugart 901

1973 237.25 kB[24][26] 3.1 megabit unformatted
8-inch: DSSD

IBM 43FD/Shugart 850

1976 500.5 kB[24] 6.2 megabit unformatted
5¼-inch (35 track) Shugart SA 400 1976[27] 87.5 kB[28] 110 kB
8-inch DSDD

IBM 53FD / Shugart 850

1977 980 kB (CP/M) – 1200 kB (MS-DOS FAT) 1.2 MB
5¼-inch DD 1978 360 or 800 kB 360 kB
3-inch 1982[29][30] 360 kB[citation needed] 125 kB (SS/SD),

500 kB (DS/DD)[30]

3½-inch SS (DD at release) 1983[31] 360 kB (400 on Macintosh) 500 kB
5¼-inch QD 720 kB 720 kB
5¼-inch RX50 (SSQD) Circa 1982 400 kB[citation needed] 400 kB
5¼-inch HD 1982[32] 1200 kB 1.2 MB
3-inch Mitsumi Quick Disk 1985 128 to 256 kB  ?
2-inch 1989 720 kB[33]  ?
2 12-inch 1986[34]  ?  ?
5¼-inch Perpendicular 1986[34] 10 MB[citation needed]  ?
3½-inch HD 1987 1440 kB (1760 kB on Amiga) 1.44 MB (2.0 MB unformatted)
3½-inch ED 1987[35] 2880 kB 2.88 MB
3½-inch Floptical (LS) 1991 20385 kB 21 MB
  • For 8-inch see Table of 8-inch floppy formats IBM 8-inch formats. Spare, hidden and otherwise reserved sectors are included in this number.



Data is generally written to floppy disks in sectors (angular blocks) and tracks (concentric rings at a constant radius). For example, the HD format of 3½-inch floppy disks uses 512 bytes per sector, 18 sectors per track, 80 tracks per side and two sides, for a total of 1,474,560 bytes per disk.[36] Some disk controllers can vary these parameters at the user's request, increasing storage on the disk, although they may not be able to be read on machines with other controllers. For example, Microsoft applications were often distributed on 3½-inch 1.68 MB DMF disks formatted with 21 sectors instead of 18; they could still be recognized by a standard controller. On the IBM PC, MSX and most other microcomputer platforms, disks were written using a constant angular velocity (CAV) format,[35] with the disk spinning at a constant speed and the sectors hold the same amount of information on each track regardless of radial location.




The raw maximum transfer rate of 3½-inch HD floppy drives and interfaces, disregarding overheads, is as much as 1000 kilobits/s, or approximately 83% that of single-speed CD‑ROM (71% of audio CD). This represents the speed of raw data bits moving under the read head; however, because of the very high amount of overhead in the system (use of soft sectors with headers, sync issues preventing sequential reads of an entire 18-sector track in a single rotation, etc.), the actual user data read/write speed is much lower. In fact, a DSHD diskette formatted with an efficient non-sequential (interleaved or "twist") sector layout could sync and read an average of only slightly more than three double-sided pairs of 512‑byte sectors per 0.2 s revolution, or a little over 15 sectors/second, for an effective data rate of approximately 125 kbit/s. At this speed, a single, disk-filling file would take a good 90 seconds to transfer; smaller or fragmented files further reduced transfer speed because of the slow head seek speed and the requirement to re-read the FAT from Track 0 along with any folder data, as removable media is rarely cached. Unusually, when compared to hard disks, optical drives and archive tapes, the floppy disk standard proper did not receive any further successful speed or capacity upgrades throughout its period of relevance, from the mid-80s introduction of DSHD through to its eventual abandonment more than 20 years later.

However, some developments did seek to improve this, but with limited success. Double-sided extended-density (DSED) 3½-inch floppy disks, introduced by Toshiba in 1987 and adopted by IBM on the PS/2 in 1994, doubled the number of sectors per track, thereby providing double the data rate and capacity of conventional DSHD 3½-inch drives.[35] Although it was not enabled by default, both the MS‑DOS / Windows 3.1 "Smartdrive" caching TSR and the system cache of later Windows versions can be configured to cache removable drives, including floppy disks. Similarly, some USB floppy drives use caching to increase performance while being built from standard speed drives; alternatively, the X10 accelerated floppy drive was an attempt to physically increase floppy performance by increasing spindle RPM.

More successfully, a number of (typically QIC-standard) tape-based backup drives that interfaced via the floppy drive controller were developed and sold by manufacturers such as Travan and Iomega. These made better use of the available bandwidth, and eventually pushed the 500/1000 kb/s limits of standard (DD/HD) motherboard floppy disk controllers; higher end models could make use of the 2000 kbit/s throughput of DSED controllers, and plug-in "high speed" adapter cards were offered for PCs lacking this capability. Though inadequate by modern standards, their speed was competitive with early CD recorders and Zip drives, and was sufficient for overnight backups of a contemporary home or small office user's hard drive.

See also[edit]


  2. ^ "20th century disk storage chronology". IBM archives. Retrieved 2011-07-19. 
  3. ^ "Five decades of disk drive industry firsts". www.disktrend.com (web.archive.org). Retrieved 2012-10-15. 
  6. ^ 1991 Disk/Trend Report, Flexible Disk Drives, Figure 2
  7. ^ Reinhardt, Andy (August 12, 1996). "Iomega's zip drives need a bit more zip". Business Week (The McGraw-Hill Companies) (33). ISSN 0007-7135. 
  12. ^ Landphair, Ted (10 March 2007). "So Long, Faithful Floppies". VOA News (Voice of America). Retrieved 25 December 2008. 
  15. ^ Jim Porter, ed. (2005). "Oral History Panel on 8 inch Floppy Disk Drives" (PDF). p. 4. Retrieved 2011-06-22. 
  16. ^ "Floppy Disk". Louisiana State University. 
  17. ^ IBM 3740
  18. ^ The IBM Diskette General Information Manual
  20. ^ "Managing Disks". Retrieved 2006-05-25. 
  21. ^ "A question of floppies". Retrieved 2011-02-20. 
  24. ^ a b c Research journal (PDF) .
  26. ^ Research journal (PDF) .
  31. ^ Infoworld Media Group (November 1, 1982). "Tandon announces tiny but powerful 3½ inch disk drive". InfoWorld (InfoWorld Media Group, Inc.) 4 (43): p.11. ISSN 0199-6649. 
  32. ^ per 1986 Disk/Trend Report, Flexible Disk Drives
  33. ^ "Viability of 2-Inch Media Standard for PCs in Doubt". InfoWorld 11 (31): p. 21. July 31, 1989. 
  35. ^ a b c Mueller, Scott (2004). Upgrading and Repairing PCs, 15th Anniversary Edition. Que Publishing. p. 1547. ISBN 0-7897-2974-1. Retrieved 2011-07-16. 
  37. ^ "The Original Macintosh". 
  38. ^ "PROPERTIES OF STORAGE SYSTEMS". Mt. San Antonio College. 



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