Floppy disk
From Freepedia
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 initialism not to be confused with "fixed disk drive", which is an old IBM term for a hard disk drive.
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Background
Floppy disks, also known as floppies or diskettes (a name chosen in order to be similar to the word "cassette"), were ubiquitous in the 1980s and 1990s, being used on home and personal computer ("PC") platforms such as the Apple II, Macintosh, Commodore 64, Amiga, and IBM PC to distribute software, transfer data between computers, and create small backups. Before the popularization of the hard drive for PCs, floppy disks were often used to store a computer's operating system (OS), application software, and other data. Many home computers had their primary OS kernels stored permanently in on-board ROM chips, but stored the disk operating system on a floppy, whether it be a proprietary system, CP/M, or, later, DOS.
By the early 1990s, the increasing size of software meant that many programs were distributed on sets of floppies. Toward the end of the 1990s, software distribution gradually switched to CD-ROM, and higher-density backup formats were introduced (e.g., the Iomega Zip disk). With the arrival of mass Internet access, cheap Ethernet, and USB "keydrives", the floppy was no longer necessary for data transfer either, and the floppy disk was essentially superseded.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 (LS-120) with a capacity of 120 MB (actually 120.375 MiB) while the drive was backward compatible with standard 3½-inch floppies.
Nonetheless, manufacturers were reluctant to remove the floppy drive from their PCs, for backward compatibility, and because many companies' IT departments appreciated a built-in file transfer mechanism that always worked and required no device driver to operate properly. Apple Computer was the first mass-market computer manufacturer to drop the floppy drive from a computer model altogether with the release of their iMac model in 1998, and Dell made the floppy drive optional in some models starting in 2003. To date, 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 disk sizes are almost universally referred to in imperial measurements, even in countries where metric is the standard. Formatted capacities are generally set in terms of binary kilobytes (as 1 sector is generally 512 bytes). However recent sizes of floppy are often refered to in a strange hybrid unit i.e. a "1.44 megabyte" floppy is 1.44×1000×1024 bytes, not 1.44×1024×1024 bytes nor 1.44×1000×1000.
History
The 5¼-inch minifloppy
This format is also known as 5.25-inch.
In 1975, Burroughs' plant in Glenrothes developed a prototype 5¼-inch drive, stimulated both by the need to overcome the larger 8-inch floppy's asymmetric expansion properties with changing humidity, and, to reflect the knowledge that IBM's audio recording products division was demonstrating a dictation machine using 5¼-inch disks. In one of the industry's historic gaffes, Burroughs corporate management decided it would be "too inexpensive" to make enough money, and shelved the program.
In 1976 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 (KiB) .
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, in competing physical disk formats: hard-sectored (90KB) and soft-sectored (110KB). The 5¼-inch formats quickly displaced the 8-inch from most applications, and the 5¼-inch hard-sectored disk format eventually disappeared. These early drives read only one side of the disk, leading to the popular budget approach of cutting a second write-enable slot and index hole into the carrier envelope and flipping it over (thus, the "flippy disk") to use the other side for additional storage.
Tandon introduced a double-sided drive in 1978, doubling the capacity, and a new "double density" format increased it again, to 360 KB (KiB) .
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 (KiB) . These did not see widespread use, as they were not supported by IBM in its PCs. (Another oddball format was used by Digital Equipment Corporation's Rainbow-100, DECmate-II and Pro-350. It held 400 KB (KiB) on a single side by using 96 tracks-per-inch and cramming 10 sectors per track.) In 1984, along with the IBM PC/AT, the quad density disk appeared, which used 96 tracks per inch combined with a higher density magnetic media to provide 1200 KB (1280 KiB) of storage (normally and misleadingly referred to as 1.2 megabytes). Since the usual (very expensive) hard disk held 10-20 megabytes at the time, this was considered quite spacious.
By the end of the 1980s, the 5¼-inch disks had been superseded by the 3½-inch disks. Though 5¼-inch drives were still available, as were disks, they faded in popularity as the 1990s began. The main community of users was primarily those who still owned '80s legacy machines running MS-DOS that had no 3½-inch drive; the advent of Windows 95 (not even sold in stores in a 5¼-inch version; a coupon had to be obtained and mailed in) and subsequent phaseout of standalone MS-DOS with version 6.22 forced many of them to upgrade their hardware. On most new computers the 5¼-inch drives were optional equipment. By the mid-1990s the drives had virtually disappeared as the 3½-inch disk became the preeminent floppy disk.
The 3-inch compact floppy disk
It was first introduced to the market in 1982 when Amdek released the AmDisk Micro-Floppy-disk cartridge system. Originally designed for use with the Apple II Disk II interface card, it has also been connected to other computers with success.
The drive itself was originally designed by Hitachi, Matsushita and Maxell. Only Teac outside this "network" is known to have produced drives. Similarly, only three manufacturers of media (Maxell, Matsushita and Tatung) are known (sometimes also branded Yamaha, Amsoft, Panasonic, Tandy, Godexco, and Dixons), but "no-name" disks with questionable quality have been seen in the wild.
Amstrad incorporated a 3" single-sided drive into their CPC and PCW lines, and this format and the drive mechanism was later "inherited" by the ZX Spectrum +3 computer after Amstrad bought Sinclair. Later models of the PCW featured double-sided, double density drives.
While all 3" media were double-sided in nature, single-sided drive owners were able to flip the disk over to use the other side. The sides were termed "A" and "B" and were completely independent, but single-sided drive units could only access the upper side at one time.
The disk format itself had no more capacity than the more popular (and cheap) 5¼" floppies. Each side held 180 KiB for a total of 360 KiB per disk, and later 720 KiB for the PCW range. Unlike 5¼" or 3½" disks, the 3" disks were designed to be reversible and sported two independent write-protect switches. It was also more reliable thanks to its hard casing (some reviews at the time reported driving over them with no problems).
3" drives were also used on a number of exotic and obscure CP/M systems such as the Tatung Einstein and occasionally on MSX systems in some regions. Other computers to have used this format are the more unknown Gavilan Mobile Computer and Matsushita's National Mybrain 3000. The Yamaha MDR-1 also used 3" drives.
Not a bad format in its own right, but the main problems were the high prices, due to the quite elaborate and complex case mechanisms, and low nominal capacities. However, the tip on the weight was when Sony in 1984 convinced Apple Computer to use the 3½" drives in the Macintosh 128K model, effectively making it a de-facto standard.
It is still possible to source new and used 3" drives from suppliers on the Internet.
Mitsumi's "Quick Disk" 3-inch floppies
Another, even less successful 3" format was Mitsumi's Quick Disk format, whose most notable use was it being used on the Famicom Disk System apart from some early MIDI keyboards and some mostly obscure Japanese computer systems. It had a 3" per 4" plastic case and was double sided, much like the most common 3" format, but with simpler shutter mechanisms [1].
The 3½-inch microfloppy diskette
This format is also known as 3.5-inch.
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.
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 irregular, rectangular shape had the additional merit that it made it impossible to insert the disk sideways by mistake, as had indeed been possible with earlier formats.)
The Shutter mechanism was not without its problems however. On old or roughly treated disks it could bend away from the disk. This made it vulnerable to being ripped off completely (which doesn't damage the disk itself but does leave it much more vulnerable to dust) or worse catching inside a drive and possiblly damaging it. If you see a disk with the cover bending away the best option is to rip the cover off (to make sure it doesn't catch in the drive) then immediately copy the data off it. Most modern floppies have a springy plastic cover that does not tend to bend away from the disk.
Like the 5¼-inch, the 3½-inch disk underwent an evolution of its own. They were originally offered in a 360 KB (KiB) single-sided and 720 KB (KiB) 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 (KiB) 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 (KiB) (normally and misleadingly referred to as 2.88 MB) introduced on the second generation NeXT Computers in 1991, and on IBM PS/2 model 57 also in 1991, but by the time it was available it was already too small to be a useful advance over 1440 KB (KiB), 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.
Trivia
- 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. The typical data transfer rate can be as much as 24 KB/s, depending on the drive unit.
- 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. In Finnish, the term is korppu (rusk, crumpet, biscuit) due to its rigidity compared to 5¼-inch lerppu (floppy).
- Even if such a format was hardly officially supported on any system, it is possible to "force" a 3½-inch floppy disk drive to be recognized by the system as a 5¼-inch 360 KB (KiB) or 1200 KB (KiB) one (on PCs and compatibles, this can be done by simply changing the CMOS BIOS settings) and thus format and read non-standard disk formats, such as a double sided 360 KB (KiB) 3½-inch disk. Possible applications include data exchange with obsolete CP/M systems, for example with an Amstrad CPC.
Contemporary 3½-inch formats
Not long after the 2880 KB (KiB) 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. None of these ever reached the point where it could be assumed that every current PC would have one and they have now largely been replaced by CD burners (which produce disks that can be read in almost any PC) and USB flash drives (which can be read and written from any PC with a USB port and a reasonably modern operating system).
Flextra
As early as 1988 Brier Technology introduced the Flextra BR 3020 which boosted 21.4 MB (marketing, true size was 21,040 KiB, 25 MiB unformatted). Later the same year it introduced the BR3225 which doubled the capacity. This model could also read standard 3½-inch disks.
Apparently it used 3½-inch disks standard disks which had servo information embedded on them for use with the Twin Tier Tracking technology.
Floptical
In 1991 Insite Peripherals' "Floptical" was the first off the blocks, offering 20, 40 and ultimately 80 MB devices that would still read and write 1440 KB (KiB) disks. However, the drives did not connect to a normal floppy disk controller (Floptical drives require a SCSI controller instead), meaning that many older PCs were unable to boot up from a disk in a Floptical drive. This again adversely affected adoption rates.
Zip drive
In 1994 Iomega introduce the Zip drive. Not true to the 3½-inch form factor, hence not compatible with the standard 1.44 MB floppies, it became the most popular of the "super floppies" and is included here for completeness. It boasted 100 MB, later 250 MB, and then 750 MB of storage and came to market at just the right time. Zip disks were very popular for several years but never reached the stage where you could assume that almost every PC would have them.
LS-120
Announced in 1995, the "SuperDisk" drive, often seen with the brand names Matsushita (Panasonic) and Imation, had an initial capacity of 120 MB (120.375 MiB) using even higher density "LS-120" disks. It was subsequently upgraded ("LS-240") to 240 MB (240.75 MiB). Not only could the drive read and write 1440 KB (KiB) disks, but the last versions of the drives could write 32 MB onto a normal 1440 KB (KiB) 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.
Sony HiFD
Factual unreliability made the Sony HiFD 150/200 MB floppy disk format, introduced in 1997/98, suffer the same destiny as the LS-variants.
Caleb Technology’s UHD144
Little is known about this device except that it surfaced early in 1998 and provided 144 MB of storage while also being compatible with the standard 1.44 MB floppies. It was slower than the competitors, but cheaper.
Structure
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 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.
Current situation
The 8-inch 5¼-inch and 3-inch formats can be considered almost totally dead. 3½-inch drives and disks are still widely available. As of 2005 3½-inch drives are still common equipment on most new PCs other than laptops. On others, they are either optional, or can be purchased as aftermarket equipment.
However, the advent of other portable storage options, such as Zip disks, USB storage devices, and recordable or rewritable CDs, and the rise of multi-megapixel digital photography have encouraged the creation and use of files larger than most 3½-inch disks can hold. In addition, the increasing availability of broadband and wireless Internet connections is decreasing the utility of removable storage devices overall. The 3½-inch floppy is growing as obsolete as its larger cousin became a decade before.
Some manufacturers have stopped offering 3½-inch drives on new computers as standard equipment. The Apple Macintosh, which popularized the format in 1984, began to move away from it in 1998 with the iMac model—possibly prematurely, since the basic model iMac of the time only had a CD-ROM drive giving users no easy access to removable media. This made USB-connected floppy drives a popular accessory for the early iMacs. In February 2003, Dell, Inc. announced that they would no longer include floppy drives on their Dell Dimension home computers as standard equipment, although they are available as a selectable option for around $20.
Compatibility
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 partially compatible. Higher density drives are built to read, write and even format lower density media without problems, provided the correct media is used for the density selected. However, if by whatever means a diskette is formatted at the wrong density, the result is a substantial risk of data loss due to magnetic mismatch between oxide and the drive head's writing attempts. Still, a fresh diskette that has been manufactured for high density use can theoretically be formatted as double density, but only provided that no information has ever been written on the disk using high density mode (for example, HD diskettes that are pre-formatted at the factory are out of the question). The magnetic strength of a high density record is stronger and will "overrule" the weaker lower density, remaining on the diskette and causing problems. However, in practice there are people who use downformatted (ED to HD, HD to DD) or even overformatted (DD to HD) without apparent problems, see the Floppy trivia section. Doing so always constitutes a data risk, so one should weigh out the benefits (e.g. increased space and/or interoperability) versus the risks (data loss, permanent disk damage).
The situation was even more complex with 5¼-inch diskettes. The head gap of a 1200 KB (KiB) drive is shorter than that of a 360 KB (KiB) 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 1200 KB 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 (KiB) 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 or scissors. 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 Distribution Media Format (DMF) disks, a hack that allowed 1.68 MB (1680 KiB) to be stored on a 3½-inch floppy by formatting it with 21 sectors instead of 18, while these disks were still properly recognized by a standard controller.) On the IBM PC and also on the MSX, Atari ST, Amstrad CPC, and most other microcomputer platforms, disks are written using a Constant Angular Velocity (CAV) – Constant Sector Capacity format. This means that the disk spins at a constant speed, and the sectors on the disk all hold the same amount of information on each track regardless of radial location.
However, this is not the most efficient way to use the disk surface, even with available drive electronics. Because the sectors have a constant angular size, the 512 bytes in each sector are packed into a smaller length near the disk's 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 64/128
Commodore started its tradition of special disk formats with the 5¼-inch disk drives accompanying its PET/CBM, VIC-20 and Commodore 64 home computers, like the 1540 and (better-known) 1541 drives used with the latter two machines. The standard Commodore Group Code Recording scheme used in 1541 and compatibles employed four different data rates depending upon track position (see zone bit recording). Tracks 1 to 17 had 21 sectors, 18 to 24 had 19, 25 to 30 had 18, and 31 to 35 had 17, for a disk capacity of 170 KB (170.75 KiB).
Eventually Commodore gave in to disk format standardization, and made its last 5¼-inch drives, the 1570 and 1571, compatible with Modified Frequency Modulation (MFM), to enable the Commodore 128 to work with CP/M disks from several vendors. Equipped with one of these drives, the C128 was able to access both C64 and CP/M disks, as it needed to, as well as MS-DOS disks (using third-party software), which was a crucial feature for some office work.
Commodore also offered its 8-bit machines a 3½-inch 800 KB (KiB) disk format with its 1581 disk drive.
The Commodore Amiga
The Commodore Amiga computers used an 880 KB (KiB) format (eleven 512-byte sectors per track) on a 3½-inch floppy. Because the entire track was written at once, inter-sector gaps could be eliminated, saving space. The Amiga floppy controller was much more flexible than the one on the PC: it did not impose arbitrary format restrictions, and foreign formats such as the IBM PC could also be handled. On the PC, however, there is no way to read an Amiga disk without special hardware or a second floppy drive ([2][3]), which is also a crucial reason for an emulator being technically unable to access real Amiga disks inserted in a standard PC floppy disk drive.
Commodore never upgraded the Amiga chip set to support high-density floppies, but sold a custom drive (made by Chinon) that spun at half speed (150 RPM) when a high-density floppy was inserted, enabling the existing floppy controller to be used. This drive was introduced with the launch of the Amiga 3000 , although the later Amiga 1200 was only fitted with the standard DD drive. The AMIGA HD disks could handle 1.6MB.
The Acorn Archimedes
Another machine using a similar "advanced" disk format was the British Acorn Archimedes, which could store 800K on a 3½-inch DD floppy using the ADFS D and E formats. Later Archimedes models and the Risc PC could also store 1600 KB on a 3½-inch HD floppy using ADFS's F format. It could also read and write disk formats from other machines, for example the Atari ST and the IBM PC. It was also capable of reading and writing the 640K format of earlier versions of ADFS for the BBC model B, B+, Master and the Acorn Electron. With third party software it could even read the BBC Micro's original single density DFS disks. The Amiga's disks could not be read as they used a non-standard sector size and unusual sector gap markers.
12-inch floppy disks
In the late 1970s some IBM mainframes also used a 12-inch (30 cm) floppy disk, but little information is currently available about their internal format or capacity.
4-inch floppies
IBM in the mid-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.
Auto-loaders
IBM developed, and several companies copied, an autoloader mechanism that could load a stack of floppies one at a time into a drive unit. These were very bulky systems, and suffered from media hangups and chew-ups more than anyone liked, but they were a partial answer to replication and large removable storage needs. The smaller 5¼- and 3½-inch floppy made this a much easier technology to perfect.
Floppy mass storage
A number of companies, including IBM and Burroughs, experimented with using large numbers of unenclosed disks to create massive amounts of storage. The Burroughs system used a stack of 256 12-inch disks, spinning at high speed. The disk to be accessed was selected by using air jets to part the stack, and then a pair of heads flew over the surface as in any standard hard disk drive. This approach in some ways anticipated the Bernoulli disk technology 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 Ion and Xapshot cameras from Canon. It was officially referred to as a Video Floppy (or VF for short).
VF was not a digital data format; each track on the disk stored one video field in the analog interlaced composite video format in either the North American NTSC or European PAL standard. This yielded a capacity of 25 images per disk in frame mode and 50 in field mode.
The same media was used digitally formatted - 720 KB (KiB) double-sided, double-density - in the Zenith Minisport laptop computer circa 1989. Although the media exhibited nearly identical performance to the 3½-inch disks of the time, it was not successful.
Ultimate capacity, speed
It is not easy to provide an answer for data capacity, as there are many factors involved, starting with the particular disk format used. The differences between formats and encoding methods can result in data capacities ranging from 720 KB (KiB) 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) 32 MB 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 (KiB) 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.
Usability
One of the chief usability problems of the floppy disk is its vulnerability. Even inside a closed plastic housing, the disk medium is still highly sensitive to dust, condensation, and temperature extremes. As with any magnetic storage, it is also vulnerable to magnetic fields. Blank floppies have usually been distributed with an extensive set of warnings, cautioning the user not to expose it to conditions which can endanger it.
Users damaging floppy disks (or their contents) were once a staple of "stupid user" folklore among computer technicians. These stories poked fun at users who stapled floppies to papers, made faxes or photocopies of them when asked to "copy a disk", or stored floppies by holding them with a magnet to a file cabinet. The flexible 5¼-inch disk could also (folklorically) be abused by rolling it into a typewriter to type a label, or by removing the disk medium from the plastic enclosure 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 trivia
- In the early days manufacturers of "single sided" floppy disks would advise consumers that they only "certified" one side (hence the name single-sided), and if the user wanted to use the other side of the diskette, they should buy the more expensive "double-sided" variety of floppy disks. Consumers quickly found out that the single-sided diskettes were certified on BOTH sides regardless, since the disk manufacturer never knew which drive mechanism would be used, and if that drive's head was on the bottom or top.
- On the disk drives of the old Atari 8-bit family of computers, the drive activity indicator LEDs were actually part of the power circuit. If they burned out, the drive would stop working.
- 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 with the Commodore 1541 and 1571 disk drives to vibrate the head carriage against a "Track-0" head stop at varying frequencies to create simple musical melodies (e.g., Amazing Grace or the James Bond Theme).
- 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 ([4], [5]). Moreover, it produces poor image quality compared to filters designed for this purpose.
- The holes on the right side of a 3½-inch disk can be altered as to 'fool' some disk drives or operating systems (others such as the Acorn Archimedes simply don't care about the holes) into treating the disk as a higher or lower density one, for backwards compatibility or economical reasons. Popular modifications include:
- Drilling or cutting an extra hole into the right-lower side of a 3½-inch DD disk (symmetrical to the write-protect hole) in order to format the DD disk into a HD one. This was a popular practice during the early 1990s, as most people switched to HD from DD during those days and some of them "converted" some or all of their DD disks into HD ones, for gaining an extra "free" 720 KiB of disk space. The success ratio was very high, especially as late DD disks used the same materials as HD ones, so they had no problem supporting the higher density. In general, only very old (made before 1989) DD disks were likely to exhibit faults and read/write errors.
- Vice versa, taping the right hole on a HD 3½-inch disk enables it to be 'downgraded' to DD format. This may sound counterproductive at first, but there are practical scenarios e.g. compatibility issues with older computers, drives or devices that use DD floppies, like some electronic music keyboards and samplers [6] where a 'downgraded' disk can be useful, as factory-made DD disks have become hard to find after the mid-1990s. See the section "Compatibility" above. It is important to note that due to read/write voltage differences in the heads of DD vs. HD disks, writing to an HD floppy with a DD drive (or an HD drive in DD mode) is widely considered to be a highly unreliable method of storing data.
- Note: By default, many older HD drives will recognize ED disks as DD ones, since they lack the HD-specific holes and the drives lack the sensors to detect the ED-specific hole. Most DD drives will also handle ED (and some even HD) disks as DD ones.
- Similarly, drilling an HD-like hole (under the ED one) into an ED (2880 KiB) disk for 'downgrading' it to HD (1440 KiB) format. This can turn useful if there are a lot of unusable ED disks due to the lack of a specific ED drive, which can now be used as normal HD disks. In general, they work pretty well.
- Finally, it is possible to "upgrade" a HD disk into an ED one by drilling an ED-positioned hole above the HD one, although the considerations made for DD vs HD disk material probably aren't valid for HD vs ED, and such "upgraded" disks probably aren't reliable.
- Double disk 'upgrades' or 'downgrades' are possible by drilling ED holes into DD disks or taping ED disks.
- New Order's classic dance track "Blue Monday" owes some of its popularity to the 12-inch version of the single initially being shipped in a sleeve designed to resemble a 5¼-inch floppy. Legend has it that it was so expensive to produce the sleeve that Factory Records lost money despite the single's runaway success. Fatboy Slim's 1995 album Better Living Through Chemistry features a 3½-inch floppy with the track names on its label as the main album art in homage to Blue Monday.
See also
- RaWrite2 (a floppy disk image file writer/creator)
- Zip drive (a newer, larger and proprietary format for removable storage)
- On Unix or Unix-like systems the dd program can be used to write an image to a floppy.
References
- Norman, Donald (1990). The Design of Everyday Things. Currency, Reissue edition. ISBN 0385267746.
- Weyhrich, Steven (2005). "The Disk II" – A detailed essay describing one of the first commercial floppy disk drives (from the Apple II History website)
- Immers, Richard; Neufeld, Gerald G. (1984). Inside Commodore DOS. The Complete Guide to the 1541 Disk Operating System. DATAMOST, Inc & Reston Publishing Company, Inc. (Prentice-Hall). ISBN 0-8359-3091-2.
- Englisch, Lothar; Szczepanowski, Norbert (1984). The Anatomy of the 1541 Disk Drive. Grand Rapids, MI: Abacus Software (translated from the original 1983 German edition, Düsseldorf: Data Becker GmbH). ISBN 0-916439-01-1.
External links
- HowStuffWorks: How Floppy Disk Drives Work – By Gary Brown.
- Computer Hope: Information about computer floppy drives – Including abbreviated history, physical parameters, and cable pin specifications.
- "There is no such thing as a 3.5 inch floppy disc." – By Jonathan de Boyne Pollard
- "There is no such thing as a 1.44MB standard format floppy disc." – By Jonathan de Boyne Pollard
- NCITS (mention of ANSI X3.162 (5¼-inch) and X3.171 (90 mm) floppy standards)
- Fujifilm Tech Support Flash (document dated 1999, still using imperial units)
- "R.I.P. Floppy Disk" – From BBC News Online
- "The Death of the Floppy Disk" – From Slashdot
- Dell Drops Floppy Drive on New Machine
