The

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...

is a data storage and transfer medium that was ubiquitous from the mid-1970s well into the 2000s. Besides the 3½-inch and 5¼-inch formats used in

IBM PC compatible IBM PC compatible computers are similar to the original IBM PC, XT, and AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such computers were referred to as PC clones, IBM clones or IBM PC clones. ...

systems, or the 8-inch format that preceded them, many proprietary floppy disk formats were developed, either using a different disk design or special layout and encoding methods for the data held on the disk.

Non-standard media and devices

IBM DemiDiskette

In the early 1980s, IBM Rochester developed a 4-inch floppy disk drive, the Model 341 and an associated diskette, the DemiDiskette. At about half the size of the original 8-inch floppy disk the name derived from the prefix ''

demi Demi is a feminine given name with Greek and Latin roots. It was originally a nickname of Demetria, the feminine form of the masculine name Demetrius, which is itself the Latin and English spelling of the Greek name Demetrios. It is also an Alba ...

'' for "half". 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 The product was announced and withdrawn in 1983 with only a few units shipped. IBM wrote off several hundred million dollars of development and manufacturing facility. IBM obtained patent number on the media and the drive for the DemiDiskette.

Tabor Drivette

Another unsuccessful diskette variant was the ''Drivette'', a 3¼-inch diskette drive marketed by Tabor Corporation of Westland, Massachusetts, USA between 1983 and 1985 with media supplied by

Dysan Dysan was an American storage media manufacturing corporation, formed in 1973 in San Jose, California, by CEO and former president C. Norman Dion of San Jose, California. It was instrumental in the development of the 5.25" floppy disk, which a ...

, Brown and 3M. The diskettes were named ''Dysan 3¼" Flex Diskette'' (P/N 802950), ''Tabor 3¼" Flex Diskette'' (P/N D3251), sometimes also nicknamed "Tabor" or "Brown" at tradeshows. The ''Microfloppy Disk Drive TC 500'' was a single-sided quad-density drive with a nominal storage capacity of 500 KB (80 tracks, 140 tpi, 16 sectors, 300 rpm, 250 kbit/s, 9,250 bpi with MFM). It could work with standard controllers for 5¼-inch floppy disks. Since August 1984, it was used in the

Seequa Chameleon 325 The Seequa Chameleon was an early 1980s luggable personal computer; it was capable of running both the DOS and CP/M operating systems. It did so by having both Zilog Z80 and Intel 8088 microprocessors.CP/M-80 &

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...

portable computer with both

Z80 The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples were ...

and 8088 processors. It was also offered in limited quantity with some PDP-11/23-based workstations by General Scientific Corporation. Originally, Educational Microcomputer Systems (EMS) announced a system using this drive as well, but later changed plans to use 3½-inch diskette drives instead.

3-inch "MCD-1 Micro Cassette"

A magnetic disk in a hard plastic shell was invented by , who was working at the Hungarian Budapest Radio Technology Factory (, BRG), in 1973. In 1982, such a product, the 3-inch MCD-1 was announced internationally and Jack Tramiel showed interest in using the technology in his Commodore computers, but negotiations fell through. Versions of the floppy drive was released in minimal quantity for the

ZX Spectrum The ZX Spectrum () is an 8-bit computing, 8-bit home computer that was developed by Sinclair Research. It was released in the United Kingdom on 23 April 1982, and became Britain's best-selling microcomputer. Referred to during development as t ...

and

Commodore 64 The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness ...

, and some computers made in East Germany were also equipped with one. The floppies are single sided and can hold up to 149 KB of data when MFM formatted. The drives were compatible with contemporary

floppy controllers A floppy-disk controller (FDC) has evolved from a discrete set of components on one or more circuit boards to a special-purpose integrated circuit (IC or "chip") or a component thereof. An FDC directs and controls reading from and writing to a ...

. Production was very limited in the early 1980s due to manufacturing problems and the product was abandoned by 1984 after the industry adopted a standard 3.5 inch format.

3-inch "Compact Floppy Disk" / "CF-2" format

Maxell Compact Floppy Disk CF2-D 20050125

The 3-inch "Compact Floppy Disk" or "CF-2" was an intended rival to Sony's 3.5" floppy system introduced by a consortium of manufacturers led by Matsushita.

Hitachi () is a Japanese multinational corporation, multinational Conglomerate (company), conglomerate corporation headquartered in Chiyoda, Tokyo, Japan. It is the parent company of the Hitachi Group (''Hitachi Gurūpu'') and had formed part of the Ni ...

was a manufacturer of 3-inch disk drives, and stated in advertisements, "It's clear that the 3" floppy will become the new standard." The format was widely used by Amstrad in their CPC and PCW computers, and (after Amstrad took over manufacture of the line) the Sinclair ZX Spectrum +3. It was also adopted by some other manufacturers/systems such as

Sega is a Japanese multinational corporation, multinational video game and entertainment company headquartered in Shinagawa, Tokyo. Its international branches, Sega of America and Sega Europe, are headquartered in Irvine, California and London, r ...

, the

Tatung Einstein The Tatung Einstein was an eight-bit home/personal computer produced by Taiwanese corporation Tatung, designed in Bradford, England at Tatung's research laboratories and assembled in Bridgnorth and Telford, England. It was aimed primarily at sm ...

, and Timex of Portugal in the FDD and FDD-3000 disk drives. Despite this, the format was not a major success. Three-inch diskettes bear much similarity to the -inch size, but with some unique features. One example is the more elongated plastic casing, taller than a -inch disk, but less wide and thicker (i.e. with increased depth). The actual 3-inch magnetic-coated disk occupies less than 50% of the space inside the casing, the rest being used by the complex protection and sealing mechanisms implemented on the disks, which thus are largely responsible for the thickness, length, and relatively high costs of the disks. On the early Amstrad machines (the CPC line and the PCW 8256), the disks are typically flipped over to change the side (acting like 2 separate single-sided disks, comparable to the "flippy disks" of -inch media) as opposed to being contiguously double-sided. Double-sided mechanisms were introduced on the later PCW 8512 and PCW 9512, thus removing the need to remove, flip, and then reinsert the disk.

Quick Disk variants

Mitsumi was a Japanese manufacturer of consumer electronic components, founded in 1954. The company was listed on the Tokyo Stock Exchange, was constituent of the Nikkei 225 stock index and provided its products through its subsidiaries in Asia, Euro ...

marketed several 3-inch diskette "Quick Disk" formats for OEM use. They used 2.8-inch magnetic discs. The OEM could decide on the outer case of the media which led to several mechanically incompatible solutions:

Famicom Disk System

The Japanese

Nintendo is a Japanese Multinational corporation, multinational video game company headquartered in Kyoto, Japan. It develops video games and video game consoles. Nintendo was founded in 1889 as by craftsman Fusajiro Yamauchi and originally produce ...

Famicom Disk System used proprietary 3-inch diskettes called "Disk Cards" between 1986 and 1990.

Smith Corona DataDisk

Many Smith Corona "CoronaPrint" word-processor typewriters used a proprietary double-sided 3-inch diskette format named "DataDisk". Confusingly, it was labelled 2.8-inch reflecting the diameter of the magnetic disk itself rather than the media's case.

Sharp 2.5-inch floppy disk

In 1986,

Sharp Sharp or SHARP may refer to: Acronyms * SHARP (helmet ratings) (Safety Helmet Assessment and Rating Programme), a British motorcycle helmet safety rating scheme * Self Help Addiction Recovery Program, a charitable organisation founded in 199 ...

introduced a 2.5-inch floppy disk format for use with their family of

BASIC BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...

pocket computer A pocket computer was a 1980s-era user programmable calculator-sized computer that had fewer screen lines, Some had only one line and often fewer characters per line, than the Pocket-sized computers introduced beginning in 1989. Manufacturers in ...

s. Two drives were produced: the

Sharp CE-1600F The Sharp PC-1600 was a pocket computer introduced by Sharp in 1986 as a successor to the PC-1500. The PC-1600 provided compatibility with its predecessor through the use of a slave CPU that could run assembly language programs targeting the older ...

and the CE-140F (chassis: FDU-250). Both took turnable diskettes named CE-1650F with a total capacity of 2×64 KB (128 KB) at bytes per side (512 byte sectors, 8 sectors/track, 16 tracks (00..15), 48 tpi, 250 kbit/s, 270 rpm with GCR (4/5) recording).

2-inch floppy disks

At least two incompatible floppy disks measuring two inches appeared in the 1980s. One of these, officially referred to as a Video Floppy (or VF for short) can be used to store video information for

still video camera A still video camera (SVC) is a type of electronic camera that takes still images and stores them as single frames of video. They peaked in popularity in the late 1980s and can be seen as the predecessor to the digital camera. However, unlike the ...

s such as the original

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

Mavica (not to be confused with later Digital

Mavica Mavica (''Magnetic Video Camera'') is a discontinued brand of Sony cameras which use removable disks as the main recording medium. On August 25th 1981, Sony unveiled a prototype of the Sony Mavica as the world's first electronic still video cam ...

models) and the Ion and Xapshot cameras from Canon. VF is not a digital data format; each track on the disk stores one video field in the analog interlaced

composite video Composite video is an analog video signal format that carries standard-definition video (typically at 525 lines or 625 lines) as a single channel. Video information is encoded on one channel, unlike the higher-quality S-Video (two channels) a ...

format in either the North American

NTSC The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...

or European PAL standard. This yields a capacity of 25 images per disk in frame mode and 50 in field mode. LT-1-disk-front

Another 2-inch format, the LT-1, is digitally formatted—720 kB, 245 TPI, 80 tracks/side, double-sided, double-density. They are used exclusively in the Zenith MinisPORT laptop computer circa 1989. Although the media exhibited nearly identical performance to the 3½-inch disks of the time, they were not very successful. This was due in part to the scarcity of other devices using this drive making it impractical for software transfer, and high media cost which was much more than 3½-inch and 5¼-inch disks of the time. Much later, another 2-inch (case size: 54.5 mm × 50.2 mm × 2.0 mm) miniature disk format was

Iomega Iomega (later LenovoEMC) produced external, portable, and networked data storage products. Established in the 1980s in Roy, Utah, United States, Iomega sold more than 410 million digital storage drives and disks, including the Zip drive floppy d ...

PocketZip The PocketZip is a medium-capacity floppy disk storage system that was made by Iomega in 1999 that uses proprietary, small, very thin, 40 megabyte, MB Disk storage, disks. Its relation to the original Zip drive, Zip drive and disk is the flopp ...

(originally named Clik!), introduced in 1999. The disks could store 40 MB. The external drives were available as

PC Card In computing, PC Card is a configuration for computer parallel communication peripheral interface, designed for laptop computers. Originally introduced as PCMCIA, the PC Card standard as well as its successors like CardBus were defined and devel ...

Type II and with

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad v ...

interface.

Extended use cases

Flippy disks

A flippy disk (sometimes known as a "flippy") is a double-sided -inch floppy disk, specially modified so that the two sides can be used independently (but not simultaneously) in single-sided drives. Many commercial publishers of computer software (mainly, relatively small programs like arcade games that could fit on a single-sided floppy disk) distributed their products on flippy disks formatted for two different brands of computer, e.g.

TRS-80 The TRS-80 Micro Computer System (TRS-80, later renamed the Model I to distinguish it from successors) is a desktop microcomputer launched in 1977 and sold by Tandy Corporation through their Radio Shack stores. The name is an abbreviation of '' ...

on one side and Apple on the other. '' Compute!'' published an article on the topic in March 1981. Generally, there are two levels of modifications: Squareholepunch

* For Disk Operating Systems that do not use the index hole in the disk to mark the beginnings of tracks, the "flippy" modification required only a new write-enable notch to be cut if the disk was designed to be written to. For this purpose, specially designed single-rectangular-hole punchers, commonly known as disk doublers, were produced and sold by third-party computer accessory manufacturers. Many users, however, made do with a standard (round) hole puncher and/or an ordinary pair of scissors for this job. * For disk operating systems that do use index sync, a second index hole window has to be punched in both sides of the jacket, and for hard-sectored formats, an additional window must be punched for the sector holes. While cutting a second notch is relatively safe, cutting an additional window into the jacket is a great peril to the disk itself. A number of floppy-disk manufacturers produced ready-made "flippy" media. As the cost of media went down and double-sided drives became the standard, "flippies" became obsolete.

Auto-loaders

IBM developed, and several companies copied, an autoloader mechanism that can load a stack of floppies one at a time into a drive. These are very bulky systems, and suffer from media hangups and chew-ups more than standard drives, but they were a partial answer to replication and large removable storage needs. The smaller 5¼- and 3½-inch floppies 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 uses a stack of 256 12-inch disks, spinning at a high speed. The disk to be accessed is selected by using air jets to part the stack, and then a pair of heads flies over the surface as in some hard disk drives. This approach in some ways anticipated the Bernoulli disk technology implemented in the

Bernoulli Box, but

head crash A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive makes contact with its rotating platter, slashing its surface and permanently damaging its magnetic media. It is most often caused by a sudden seve ...

es or air failures were spectacularly messy. The program did not reach production.

Standard floppy replacements

A number of attempts were made by various companies to introduce newer floppy-disk formats based on the standard 3½-inch physical format. Most of these systems provide the ability to read and write standard DD and HD disks, while at the same time introducing a much higher-capacity format as well. 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

optical disc In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces. ...

burners and flash storage. Nevertheless, the 5¼- and 3½-inch sizes remain to this day as the standards for

drive bay A drive bay is a standard-sized area for adding hardware to a computer. Most drive bays are fixed to the inside of a case, but some can be removed. Over the years since the introduction of the IBM PC, it and its compatibles have had many form f ...

s in computer cases, the former used for optical drives (including

Blu-ray The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and capable of sto ...

), and the latter for

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

s. The main technological change for the higher-capacity formats 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 feedforward (blind) positioning by a stepper motor in order to position their heads over the desired track. For good interoperability of disks among drives, this requires precise alignment of the drive heads to a reference standard, somewhat similar to the alignment required to get the best performance out of an audio tape deck. The newer systems generally use position information on the surfaces of the disk to find the tracks, allowing the track width to be greatly reduced. In 1990, an attempt was made to standardize details for a 20 megabyte 3½-inch format floppy. At the time, "three different technologies that are not interchangeable" existed. One major goal was that the to-be-developed standard drive be backward compatible: that it be able to read 720 KB and 1.44 MB floppies. From a conceptual point of view, superfloppies are treated as unpartitioned media. The entire media forms a single volume.

Flextra

As early as 1987, Brier Technology announced the Flextra BR3020, which boasts 21.4 MB (a value used for marketing: its true size is 21,040 kB, 2 sides × 526 cylinders × 40 sectors × 512 bytes or 25 MB unformatted). Around 1990, it announced the BR3225 drive, which was supposed to double the capacity and also read standard DD, HD and ED 3½-inch disks. However, the drive was still not released in 1992. It uses 3½-inch standard disk jackets whose disks have low-frequency magnetic servo information embedded on them for use with the Twin-Tier Tracking technology. Media were manufactured by Verbatim. Quantum sold the drives under the QuadFlextra name.

Floptical

In 1991, Insite Peripherals introduced the " Floptical", which uses an

infra-red Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

to position the heads over marks in the disk surface. The original drive stores 21 MB, 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 are attached to the system using a

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

connector instead of the normal floppy controller. This meant that most PCs were unable to boot from them. This again adversely affected pickup rates. Insite licensed their technology to a number of companies, who introduced compatible devices as well as even larger-capacity formats. The most popular of these, by far, was the LS-120, mentioned below.

Zip drive

In 1994,

introduced the

Zip drive The Zip drive is a removable floppy disk storage system that was introduced by Iomega in late 1994. Considered medium-to-high-capacity at the time of its release, Zip disks were originally launched with capacities of 100 MB, then 250 ...

. Although neither size (the original or the later Pocket Zip drive) conforms to the 3½-inch form factor and hence is not compatible with standard 1.44 MB drives, the original physical size still became the most popular of the "super floppies". The first version boasted 100 MB; later versions boasted 250 MB and then 750 MB of storage, until the

(formerly known as Clik!) was developed with 40 MB. Though Zip drives gained in popularity for several years they never reached the same market penetration as standard floppy drives, since only some new computers were sold with the drives. The rise of

desktop publishing Desktop publishing (DTP) is the creation of documents using page layout software on a personal ("desktop") computer. It was first used almost exclusively for print publications, but now it also assists in the creation of various forms of online c ...

and

computer graphics Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great de ...

led to much larger file sizes. Zip disks greatly eased the exchange of files that were too big to fit on a standard 3.5-inch floppy or an email attachment, when there was no high-speed connection to transfer the file to the recipient. Eventually the falling prices of

compact disc The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then rele ...

optical media and, later, flash storage, along with notorious hardware failures (the so-called "

click of death Click of death is a term that had become common in the late 1990s referring to the clicking sound in disk storage systems that signals a disk drive has failed, often catastrophically. The clicking sound itself arises from the unexpected movemen ...

"), reduced the popularity of the Zip drive.

LS-120/LS-240

Announced in 1995, the "

SuperDisk The SuperDisk LS-120 is a high-speed, high-capacity alternative to the 90 mm (3.5 in), 1.44 MB floppy disk. The SuperDisk hardware was created by 3M's storage products group Imation in 1997, with manufacturing chiefly by ...

" marketed as the LS-120 drive, often seen with the brand names Matsushita (Panasonic) and Imation, had an initial capacity of 120 MB (120.375 MB). LS in this case stands for LASER-servo, which uses a very low-power superluminescent LED that generates light with a small focal spot. This allows the drive to align its rotation to precisely the same point each time, allowing far more data to be written due to the absence of conventional magnetic alignment marks. The alignment is based on hard-coded optical alignment marks, which meant that a complete format can safely be done. This worked very well at the time and as a result failures associated with magnetic fields wiping the Zip drive alignment Z tracks were less of a problem. It was also able to read and write to standard floppy disks about 5 times as fast as standard floppy drives. It was upgraded (as the "

LS-240 The SuperDisk LS-120 is a high-speed, high-capacity alternative to the 90 mm (3.5 in), 1.44 MB floppy disk. The SuperDisk hardware was created by 3M's storage products group Imation in 1997, with manufacturing chiefly by ...

") to 240 MB (240.75 MB). Not only can the drive read and write 1,440 kB disks, but the last versions of the drives can write 32 MB onto a normal 1,440 kB disk. Unfortunately, popular opinion held the Super Disks to be quite unreliable, though no more so than the

s and SyQuest Technology offerings of the same period and there were also many reported problems moving standard floppies between LS-120 drives and normal floppy drives. This belief, true or otherwise, crippled adoption. The

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

of many motherboards even to this day supports LS-120 drives as a boot option. LS-120 drives were available as options on many computers, including desktop and notebook computers from

Compaq Computer Corporation Compaq Computer Corporation (sometimes abbreviated to CQ prior to a 2007 rebranding) was an American information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced ...

. In the case of the Compaq notebooks, the LS-120 drive replaced the standard floppy drive in a multibay configuration.

Sony HiFD

Sony introduced its own floptical-like system in 1997 as the "150 MB

Sony HiFD The Sony HiFD (High capacity Floppy Disk) was a high-capacity floppy disk system developed by Sony and Fujifilm and introduced in late 1998. Development and sale of the drives was discontinued by early 2001. Announced in October 1997, HiFD disks ...

" which was originally supposed to hold 150 MB (157.3 decimal megabytes) of data. Although by this time the LS-120 had already garnered some market penetration, industry observers nevertheless confidently predicted the HiFD would be the real standard-floppy-killer and finally replace standard 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 reengineered the device for a quick rerelease, but then extended the delay well into 1998 instead, and increased the capacity to "200 MB" (approximately 210 decimal megabytes) while they were at it. By this point the market was already saturated by the Zip disk, so it never gained much market share.

Caleb Technology’s UHD144

The UHD144 drive surfaced early in 1998 as the ''it'' drive, and provides 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 US$8 at introduction and US$5 soon after.

Custom formatting types on 3½-inch and 5¼-inch media

Commodore 64/128

Commodore started its tradition of special disk formats with the 5¼-inch disk drives accompanying its PET/CBM,

VIC-20 The VIC-20 (known as the VC-20 in Germany and the VIC-1001 in Japan) is an 8-bit home computer that was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the PE ...

and

home computers, the same as the

1540 Year 1540 ( MDXL) was a leap year starting on Thursday (link will display the full calendar) of the Julian calendar. Events January–June * January 6 – King Henry VIII marries Anne of Cleves, his fourth Queen consort; the ma ...

and

1541 __NOTOC__ Year 1541 ( MDXLI) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. Events January–June * February 12 – Pedro de Valdivia founds Santiago del Nuevo Extremo, whi ...

drives used with the later two machines. The standard Commodore Group Coded Recording (GCR) scheme used in 1541 and compatibles employed four different data rates depending upon track position (see ''

zone bit recording In computer storage, zone bit recording (ZBR) is a method used by disk drives to optimise the tracks for increased data capacity. It does this by placing more sectors per zone on outer tracks than on inner tracks. This contrasts with other approach ...

''). 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 170.75 KB (175 decimal kB). Unique among personal computer architectures, the operating system on the computer itself is unaware of the details of the disk and filesystem; disk operations are handled by

Commodore DOS Commodore DOS, also known as CBM DOS, is the disk operating system used with Commodore's 8-bit computers. Unlike most other DOSes, which are loaded from disk into the computer's own RAM and executed there, CBM DOS is executed internally in the dr ...

instead, which was implemented with an extra MOS-6502 processor on the disk drive. Many programs such as

GEOS #REDIRECT GEOS {{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...

bypass Commodore's DOS completely, and replace it with fast-loading (for the time) programs in the 1541 drive. Eventually Commodore gave in to disk format standardization, and made its last 5¼-inch drives, the

1570 __NOTOC__ Year 1570 ( MDLXX) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. Events January–June * January 8 – Ivan the Terrible begins the Massacre of Novgorod. * Januar ...

and

1571 Year 1571 ( MDLXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. Events January–June * January 11 – The Austrian nobility are granted freedom of religion. * January 23 &nd ...

, compatible with Modified Frequency Modulation (MFM), to enable the

Commodore 128 The Commodore 128, also known as the C128, C-128, C= 128,The "C=" represents the graphical part of the logo. is the last 8-bit home computer that was commercially released by Commodore Business Machines (CBM). Introduced in January 1985 at the ...

to work with

CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...

disks from several vendors. Equipped with one of these drives, the C128 is able to access both C64 and CP/M disks, as it needs to, as well as MS-DOS disks (using third-party software), which was a crucial feature for some office work. At least one commercial program, ''Big Blue Reader'' by SOGWAP software was available to perform the task. Commodore also developed a 3½-inch 800 KB disk format for its

8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...

machines with the

1581 1581 ( MDLXXXI) was a common year starting on Sunday (link will display the full calendar) in the Julian calendar, and a common year starting on Thursday (link will display full calendar) of the Proleptic Gregorian calendar. Events Ja ...

disk drive, which uses only MFM. The GEOS operating system uses a disk format that is largely identical to the Commodore DOS format with a few minor extensions; while generally compatible with standard Commodore disks, certain disk maintenance operations can corrupt the filesystem without proper supervision from the GEOS kernel.

Atari 8-bit line

The combination of DOS and hardware (810, 1050 and XF551 disk drives) for Atari 8-bit floppy usage allows sectors numbered from 1 to 720 (1040 in the 1050 disk drive, 1440 in XF551). For instance, the DOS's 2.0 disk bitmap provides information on sector allocation, counts from 0 to 719. As a result, sector 720 cannot be written to by the DOS. Some companies used a copy-protection scheme where hidden data was put in sector 720 that cannot be copied through the DOS copy option. Another more-common early copy-protected scheme simply does not record important sectors as allocated in the VTOC, so the DOS Utility Package (DUP) does not duplicate them. All of these early techniques were thwarted by the first program that simply duplicated all sectors. Later DOS versions (3.0 and later 2.5) and DOSes by third parties (i.e. OSS) accept (and format) disks with up to 1040 sectors, resulting in 130 KB of storage capacity per disk side on drives equipped with double-density controllers (''i.e''. not the Atari 810) vs. previous 90 KB. That unusual 130 KB format and was introduced by Atari with the 1050 drive with the introduction of DOS 3.0 in 1983. A true double-density Atari floppy format (from 180 KB upwards) uses 128-byte sectors for sectors 1-3, then 256-byte sectors for the rest. The first three sectors typically contain boot code as used by the onboard ROM OS; it is up to the resulting boot program (such as SpartaDOS) to recognize the density of the formatted disk structure. While this format was developed by Atari for their DOS 2.0D and their (canceled) 180 KB Atari 815 floppy drive, that double-density DOS was never widely released and the format was generally used by third-party DOS products. Under the Atari DOS II scheme, sector 360 is the VTOC sector map, and sectors 361-367 contain the file listing. The Atari-brand DOS II versions and compatible use three bytes per sector for housekeeping and to link-list to the next sector. Later, mostly third-party DOS systems added features such as double-sided drives, subdirectories, and drive types such as 720 KB, 1.2 MB, 1.44 MB. Well-known 3rd party Atari DOS products include SmartDOS (distributed with the Rana disk drive), TopDos, MyDos and SpartaDOS.

Commodore Amiga

The Commodore Amiga computers use an 880 KB format (11×512-byte sectors per track, times 80 tracks, times two sides) on a 3½-inch floppy. Because the entire track is written at once, intersector gaps can be eliminated, saving space. The Amiga floppy controller is basic but much more flexible than the one on the PC: it is free of arbitrary format restrictions, encoding such as MFM and GCR can be done in software, and developers were able to create their own

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