Diskette

Summary of the history of the diskette

The diskette was launched by IBM in 1971 (in its version 8 inches) to store the microprograms of the systems 370 and, incidentally, to send for low costs of the updates to their owners. This first diskette could store 80.000 characters, that is to say approximately a day of striking of a data entry operator. For this reason, materials of seizure on diskette started to replace cumbersome and noisy the drilling machines of charts used up to that point.

The second generation of diskettes to the format of 5 inches 1/4, and was used inter alia on the APPLE II. It is it which, formatted in 360 KB equipped the IBM PC in 1981, then into 1,2 Mo PC/AT in 1983.

The third generation had an envelope which was not any more flexible paperboard, but of rigid plastic. Introduced into world PC in 1987 for the series IBM PS/2 of versions 720 KB and 1,44 Mo; the latter started to be détrônée in 2004 by key USB, since BIOS make it possible to start the computer ( booter ) starting from these keys. There existed a version 2,88 Mo which was not essential.

Another diskette of third generation also appeared on the personal computers. This one is of format 3 inches and makes it possible to store 320 KB per face. The readers for this type of diskette not being double face, it is necessary to turn over the disc to use all its capacity. This diskette was mainly used on Amstrad CPC and Oric.

Principle of operation

Physical structure

The diskettes have the same structure as the hard drives. The difference between the two is that the diskettes are removable and that it are made up only of one disc.

The diskettes are divided into tracks: left concentric circles distributed with intervals regular on their magnetic surface.

The tracks are numbered of 0 with N, the number of tracks being n+1, varying with the type of diskette. Track 0 is that located more at the outside of the diskette.

Each track is divided into a constant number of sectors of equal size. The number of these sectors depends on the format on the diskette and are numbered from 1 to N, N being the number of sectors per track. Certain computers (Macintosh, commodore) were equipped with a manager of disc supporting a variable number of sectors, this one being proportional to the length of the track, which makes it possible to increase storage capacity.

Each sector represents 512 bytes for a PC and Atari ST The sector (or block) is more the small portion of the disc that the computer can read.

The diskette is often divided into two numbered faces 0 and 1 because the recent readers are equipped with two read/write heads: for each face.

One can thus calculate the capacity of a diskette by the formula: Many faces × many tracks × many sectors/track × 512 bytes/sector .

Characteristics of some diskettes

Logical organization of a diskette to format PC

The organization of a diskette PC compatible is done in four parts:

the sector of starting ( boot ): located on the 1st sector of the track n°0 of the head n°0, one finds there information concerning the type of media, the serial number of the disc, the number of sectors per track, the number of tracks, the number of read/write heads, an optional sector of starting (diskette of starting), and references to the other sections of the diskette.
the table of allowance of the files (FAT): The FAT is an index recording the site of the files (or their fragments) on the disc. By consulting the FAT, the computer can determine if a sector available, is used or defective. The FAT is written in two copies on the disc, making it possible the utilities of diagnosis to detect errors by comparing the copies.
the root directory: One finds information there on volume, the sub-directories and the files: name, size, date/time of creation and modification, attributes (files, reading alone, hidden, system) and especially, a pointer towards the sector where it is stored.
data: The space remaining of the disc is used to store the data of the files.

Reading and writing

The disk drive is composed of two engines:

the first actuates the diskette and turns at a speed of 300 turns/minute. As soon as the computer orders a function, the diskette turns and remains a certain up time after the operations to allow a faster access to other calls (not of waiting). This number of revolutions is regulated thanks to a sensor which detects a complete rotation of the disc.
the second is an engine step by step which makes it possible to precisely move the read/write head on the desired track.

The read/write head made up of two equal reels is placed in opposite direction what allows the reading and the writing of bit, the diskette being covered with a magnetic oxide coating.

A bit is positioned or not according to the direction of the orientation of the magnetic oxide microparticles, in a direction, the bit is read like one “0” logic, and in the other direction like one “1” logic. For the writing, the head imposes a direction on the microparticles thanks to magnetic fields creates with a reel or the other following the direction which one wants to give to the written bit.

Towards a new diskette, the microparticles are directed by chance, it is thus illegible. To write on a diskette, it should as a preliminary be formatted to give him a format of data: to create the sector BOOT, the FAT and repertory ROOT in the case of a diskette FAT.

The formatting can also make a diskette bootable (it will make it possible to start the computer) by copying part of the operating system and by creating a programme of launching on the level of the BOOT, it is there that one finds the viruses most dangerous because this program is the first launched by the computer before the system.

History

The diskette 8 inches

In 1967, the development center of the devices of storage of IBM to San Jose in California accepted a new task: to develop a simple and inexpensive system to charge with the Microcodes in the Mainframe S System/370. The 370 were the first machines of IBM to use memory with Semi-conducteur S. This memory being volatile, all microcodes it was to be reloaded with each time the supply was cut off. Normally this task fell on various readers of Magnetic band who were provided almost systematically with the 370. However, the bands were long, and thus their loading was slow. IBM wished to set up a faster and adapted system, and which in addition could also make it possible to send updates to the customers at a moderate cost (about 5 dollar S).

David Noble, which worked under the direction of Alan Shugart, studied the existing solutions containing magnetic bands, in the hope to improve this type of systems. In the final analysis, it gave up this way and set out again on new bases. Its result was a floppy disc in reading alone of 8 inch S (20 Centimètre S) which it called memory the “disk” (disc-memory), which could contain 80 kilobytes data. At the beginning, it was quite simply about a disc. However, the disc was dirtied quickly, which posed problems of reading. This is why it was locked up in a plastic envelope of which the interior was covered of a fabric to capture dust. This new device equipped out of standard the 370 starting from 1971.

In 1973, IBM left a new version the floppy disc, this time on the system of data capture 3740. The new system used a format of different recording which could store up to 256 KB on the same discs, and had moreover a read/write mode. These readers spread themselves, and were finally used to transport data, replacing almost completely the magnetic bands for the small transfers.

When the first Micro-ordinateur S were developed in the Années 1970, the floppy disc of 8 inches was used on some of them like device of storage at “high-speed”. This device was very expensive. The first Operating system for microcomputers, CP/M, was distributed at the origin on discs 8 inches. However, the readers were always very expensive, practically more expensive than the computer to which they were connected. This is why the majority of the machines of this time rather used recording with cassettes.

At that time, Alan Shugart left IBM and made a short stay at Mémorex. Then, it founded Shugart Associates in 1973. The company started to work with the improvements of the existing format 8 inches and created even a new formatting of 800 KB. However, as the benefit were not with go, Shugart was congédié in 1974 by the company which it had created.

The minidiskette of 5" ¼

In 1976, one of associated with Shugart, Jim Adkisson, was approached by An Wang Wang laboratories, which felt that the format 8 inches was simply too large for the machines of word processing of office which it developed. After a meeting in a bar with Boston, Adkisson required of Wang of which size he thought that the discs should be, and Wang showed a towel and says “about this size”. Adkisson brought back the towel to California, it found that it measured 5" ¼ broad (5 inches a quarter, is approximately 13 centimetres), and developed a new reader of this size storing 110 KB.

The reader of 5" ¼ was considerably less expensive than the readers 8 inches of IBM and it started soon to appear on machines CP/M. At one time, Shugart Associates produced 4000 readers per day. In 1978, there was more than 10 manufacturers producing of the disk drives 5" ¼ and the format quickly replaced the 8 inches for the diffusion of the majority of the applications.

Tandon introduced a reader doubles face in 1978, doubling the capacity, and new format “DD” (double density) of 360 KB was essential quickly. At the beginning of the Years 1980, readers of 96 TPI ( track per inch , tracks per inch) appeared, passing the capacity from 360 to 720 KB, but this format did not have much success. In 1984, with its top-of-the-range computer PC/AT, IBM launched disc “HD” ( high density , high density). This disc, of quadruple density, used 96 tracks per inch combined with a higher density on each track; finally, it contained up to 1,2 megabytes (Mo) of data. At the time when the average hard drive contained 10 to 20 megabytes, this was regarded as rather roomy. But its use was limited to the computers equipped with a reader ad hoc .

Disk drives 5" ¼ allowed the reading and the writing. To avoid writing inadvertently on a diskette, it was enough to cover a notch, located in top on the right of the envelope of the diskette, by a sticking opaque bit of paper (the diskette “was protected in writing”). Once this removed paper, the reader could again write on the diskette.

Since the beginning, by economy, the disk drives comprised only one play-back head; the reading of the diskettes was thus done on only one face. However the two faces were covered with a magnetic medium. The salesmen of diskettes then diffused diskettes “doubles face” which comprised a notch on each side of the envelope. It was enough to remove the diskette of the reader and to turn over it to profit from a new storage capacity, on the model of the operation of the audio cassettes (before the invention of the autoreverse ). The price of the diskettes doubles face was appreciably higher than the “simple face” whereas the only difference was the additional notch. In fact of many data processing specialists bored their diskettes simple face of a new notch of the other with dimensions in order to profit from the two faces.

During the Years 1970 and 1980, the hard drives, too expensive, were quasi non-existent on the microcomputers, the flexible disk player was the device of basic primary education storage. The Operating system was to be charged in Random access memory with each starting by means of a diskette; this diskette was then removed and replaced by another container the programs and the data. Some machines using two disk drives (or a reader doubles) made it possible the user to leave the diskette of the operating system in place and to change independently the diskettes of data. To have two readers also allowed to recopy its data (the Sauvegarde R) much more effectively than with only one reader. Indeed, the system read some bytes of the diskette of origin then asked for the diskette of safeguard to write these bytes, which imposed many to and from between the diskettes. One “played toaster”. In addition to time that took, the risk to be mistaken in diskette was not negligible and handling caused wear. With two readers, it was enough to put the diskette of origin in a reader and the diskette of safeguard in the other.

Towards the end of the Years 1980, the diskettes 5" ¼ was replaced by diskettes 3 ½ inches. The popularity of the first dropped at the beginning of the Années 1990, although diskettes and readers of 5" ¼ is still available. On the majority of the new computers the readers 5" ¼ was optional devices. In the middle of the Années 1990 these readers had practically disappeared while disc 3 ½ inches became the dominating disc.

Microdiskette 3 " ½ and other diskettes out of rigid case

At the beginning of the Years 1980, limitations of the format 5" ¼ is felt more and more with the wire of the rise to power of the machines. A certain number of solutions appear then: readers of 2" , 2" ½, 3" and 3" ½ (50, 60,75 and 90 mm), developed by various companies. These solutions shared a certain number of advantages compared to the older formats: a smaller size, a rigid box of protection and a slide of protection against the writing. Amstrad chooses for reasons of cost price a reader 3" with simple face of 160 KB for the range of CPC and PCW. This format and its mechanism of drive were related to the computer ZX Spectrum +3 after Amstrad had repurchased Sinclair Research. However, the price of the readers 3" was advantageous because this format had not been essential. In fact, the users encountered great difficulties of supply diskettes, which defrayed the chronicle. The diskettes 3" remained expensive because of this shortage, making in the final analysis disappear the format for good.

The situation was different in 1984 when the company Apple selected the format of Sony 90.0 mm × 94.0 mm for the range of computers Macintosh, thus pushing this physical format with becoming the standard with the the United States. One can note besides that it is about a “quiet” passage of the imperial system (8 inches) with the Metric system (94 mm). However, the product was launched under the name of “diskette 3" ½”, for underlining the fact well that it was smaller than the 5" ¼ existing and not to divert the users accustomed to the imperial measures. Besides one of the arguments Marketing put ahead the fact that this diskette was designed to hold in a pocket of short-sleeved shirt " of size américaine". In 1989, sales of diskettes 3" ½ exceeded those of the 5" ¼: PS/2 of IBM had adopted this physical format, although with a denser formatting (1,44 Mo or place of 800 KB, and 720 K for the cut-rate version of the model of line entry).

The diskettes 3" ½ has, thanks to their rigid box and with their shutter of protection out of metal, the great advantage of protecting the faces very well from the disc against the physical contacts with the user. This shutter closes again the plastic case of the diskette with each time it is handled apart from the reader. When it is inserted, the shutter is opened by the mechanism of the reader, which makes it possible the read/write head to reach magnetic surfaces. The rectangular shape of the diskette is another advantage: it prevents from inserting the diskette in the bad direction in the reader, which was possible with the diskettes 5" ¼.

Like the diskette 5" ¼, the diskette 3" ½ evolved/moved during its existence. In the beginning, two formats were available: double density with double face of 720 KB and simple face in 360 KB (by using the same format as the diskettes of 5" ¼). The diskette was the same one, the difference being only on the level of the reader, according to whether it had only one play-back head, or for each face of the diskette. A new format called “high density” (“HD”), allowing the storage of 1,44 Mo of data (name marketing because actually, it contains 1.474.560 bytes, which is equivalent to 1440 kibi-bytes (KiB) or 1,41 MIB and 1,47 Mo into decimal). This format was presented in the middle of the Années 1980; IBM used it on the series of PS/2 presented in 1987, Apple used it in 1988 on the Macintosh IIx. Another projection in the oxide coatings made it possible to create a new format known as “extended density” (“ED”) of 2,88 Mo. This format was presented on the NeXT of second generation in 1991. However, it was already exceeded because too small at the time of its exit and thus it forever used in significant proportions. In other formats, such as that of Macintosh, the capacity of the discs doubles density reached 800 KB, but at the price of an incompatibility with models PC. Indeed, this was obtained grace the use of an engine at variable speed, making it possible to place a greater number of data on the external tracks: the readers for PC, equipped with an engine at fixed speed, were thus physically unable to read these diskettes. On Amiga, the capacity of a disc doubles density went up to 880 KB (1,76 Mo in high density), even to 980 KB by using a specific formatting.

The IBM computers always kept a characteristic, which was of being able on request to format in 1,44 Mo a diskette of 720 KB. The users used and misused this property (for reasons of marketing, 720 K, although coming from very the production lines, were then less expensive), which posed problem when they changed manufacturer thereafter. The only solution was then to bore a hole in the casing with a small gimlet so that the diskette of 720 seems one 1,44 Mo.

More than one decade after, the readers 3" ½ is always sold and equips the near total with the computers. The format is always that which was standardized in 1989 under the name ISO 9529-1.2. But these readers are proposed more and more in option. Indeed, with the arrival of other storage systems, such as the diskettes ZIP, the keys USB, CD-R, the CD-RW, the DVD, and especially the file-sharings via a network, the diskette 3" ½ becomes obsolete.

In short

Various formats are distinguished:

200 mm (8 inches): oldest; the two notches on both sides of the window of reading were the subject of a Brevet, they divided by two the tensions of the disc in the event of involuntary torsion during transport and without them, the diskettes quickly became unusable.
130 mm (5 inches a quarter), which known a great success following its adoption by the APPLE II, then by PC in 1981, but périma immediately in 1987 with the launching of the PS/2, because of its big size and incidentally of its low capacity (360 KB). The PC/AT launched in 1983 had of the same diskettes format external but of capacity 1,2 Mo and different manufacture.
80 mm (3 inches), launched by Amstrad on the computers CPC 664.
90 mm (3 inches and half)

invented by Sony,
presents the merit to hold in a small pocket of shirt (it was conceived for that)
used in version 400 KB for the Macintosh in 1984,
introduced into world PC in 1987 for the series IBM PS/2 of versions 720 KB and 1,44 Mo; the latter starts to be détrônée in 2004 by key USB, since the BIOS allow booter on these keys.
its version 2,88 Mo, used on certain PS/2 from high-end and IBM RS/6000, never met success.

Storage capacity gradually increased to reach 1,47 Mo (1,41 Me) for the last generations of diskettes (and double for a format suitable for IBM). On Commodore Amiga, it was even possible to format these same diskettes 3" 1/2 in FFS (Fast Spins System) to reach a size of 900 KB per face and even 1,8 Mo for the double density. Beyond, there exist the discs Iomega Zip, Jazz and MO (magneto-optical). Syquest also produced large diskettes capacity of the Zip type in the middle of the Années 1990, whose advantage was to have same dimensions as the diskettes 3" ½ of 1,44 Mo, of fate which a reader LS-120 could read this news high capacity but also oldest (whereas discs ZIP thickness doubles was incompatible with the old diskettes), however this format was a commercial failure.

The peripheral of reading and writing associated names disk drive .

The success of the diskette is due to its low costs and its easy transport. Its major disadvantages are its brittleness and its low storage capacity. The appearance of new supports of Sauvegarde which combine these advantages without the disadvantages makes that the diskettes are hardly any more used today: for the distribution of commercial products (software, encyclopedias), CD-ROM and DVD-ROM are less expensive than a diskette, more reliable and transport a quantity of information 500 times larger for CD and 4000 times larger for the DVD. For data storage personal, key USB make it possible to store more, better, less expensive, more quickly and in addition in a perfect silence. However, the diskettes remain practical because universal for the transfer of small files or delivered like supports of pilots with certain peripherals, in particular of the expander cards. But in the actual position of technologies, its days are counted, and one sees more and more microcomputers sold without disk drive, or option.

See too

Random access memory
Read-only memory
the diskette was during several years a means of safeguard of video games
Master Boot Record
binary Préfixes
Virus of boot

Simple: Floppy disk

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