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Floppy disk

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5 inch floppy disk

3 inch (90mm) floppy disk

A floppy disk is a type of data storage device that comprises a circular piece of thin, flexible (hence the name) magnetic media encased in a square or rectangular plastic wallet. The fact that the exterior aspect is not circular confuses some novice users. Floppy disks are read and written by a floppy disk drive or FDD, not to be confused with "fixed disk drive" which is an old IBM term for a hard disk.

Floppy disks, also known as floppies or diskettes (to be similar to cassette), were ubiquitous in the 1980s and 1990s, being used on personal computer platforms such as the IBM PC to distribute software, transfer data between computers, and create small backups[?]. Before the advent of the hard drive, floppy disks were used to store a computer's operating system and software.

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 Zip disk[?]). With the arrival of mass Internet access and cheap ethernet, the floppy was no longer necessary for data transfer either, and the floppy disk was essentially superseded. Mass backups are made to high capacity tape drives (such as DAT) or written to compact disc using CD-Writers.

Nonetheless, manufacturers were reluctant to remove the floppy drive from their PCs, for backwards compatibility. Apple Computer was the first to eschew the floppy altogether with the release of their iMac model in 1998: it had no floppy disk drive. In March of 2003, Dell Computer made a similar decision to make floppy drives optional on its higher-end computers, a move widely hailed as the end of the floppy disk as a mainstream means of data storage and exchange.

History The original floppy disk was the eight-inch. These large disks predate the desktop machine and were mainly used for transferring data between mainframe machines. Their capacity was extremely limited by today's standards, with 160 kilobytes available. The reason for the name floppy was that the exterior casing was only soft flexible plastic, leaving them vulnerable to manhandling.

Home computer manufacturers, who had previously been using magnetic tape (compact cassette) to save data, saw the possibilities for this medium.

The first floppy disk that was used in home machines was the 5¼". Small enough to fit in a desktop unit, the usual incarnation offered 360kB of storage space. Since these machines had no hard disk, the operating system would have to be loaded on one disk and then removed and replaced by another disk containing the application. Later machines using two disk drives enabled the user to leave the operating system disk in one drive and only change the application disk. These disks were also flexible and were usually contained within individual paper envelopes. The much later Quad Density disk provided 1.2 megabytes of information on one disk.

Amstrad incorporated a 3-inch disk drive into their CPC664 and CPC6128 models, amongst other manufacturers. They remained expensive and did not become standardised. However, they had a small form factor and a rigid case with a slideable write-protect[?] catch, features which would be seen later in the 3½" disk.

But by this time, the 90mm disk was arriving. American computing manufacturers called it a "3½ inch" disk (although 3.50 inches is actually 88.9mm), and the name has stuck even in countries that normally use the metric system. Borrowing from the advances made in the three-inch disks, as well as enhanced methods of manufacturing, they were able to contain 720kB of data in their first standard, Double Sided Double Density (when formatted to MS-DOS; Amiga floppies carried 880k, and early Apple floppies carried 800k). However, there was soon a new standard - High Density - represented by a human-readable stylised 'HD' in the top right of the disk and a machine-readable hole in the bottom left corner, with the write-protect catch remaining in the bottom-right corner. These were capable of 1.44MB (1.76MB on Amiga), and remain the standard in floppy disks until this day (2002), despite successful attempts to put 2.88MB on a disk via enhanced formatting techniques and use of special oxide coatings. Microsoft applications were often distributed on 'Microsoft distribution format' disks, a hack that allowed 1.68MB to be stored on a 1.44MB disk by formatting it with 21 sectors instead of 18. The most often used file system on floppy disks is FAT12.

Structure

The 5¼" disk had a large circular hole in the centre 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 media 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 writeable, detected by a photo transistor above it. Another LED/phototransistor pair located near the centre of the disk could detect a small hole, 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. Very early 5¼" disks also had holes for each sector. 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 usually 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 disk is made of two pieces of rigid plastic, with the fabric-media-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. A notch top right ensures that the disk is not inserted incorrectly, 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. Macintosh computers typically contained "Automatic" floppy disk drives, which used a motorized mechanism to eject disks. This mechanism was triggered through software, rather than a control on the drive itself.

Compatibility

Obviously, the three physical sizes of floppy disks are incompatible, and disks can only be loaded on the correct size of drive. However there are many more subtle incompatibilities.

Apple Macintosh computers can read, write and format IBM-format 3½" diskettes, provided suitable software is installed. However, many IBM-compatible computers use floppy disk drives that are physically unable to use Apple-format disks.

Within the world of IBM-compatible computers, the three densities of 3½" floppy disks are partly compatible. Higher density drives are built to read, write and even format lower density media without problems, provided the correct media is used for the density selected. However, if by whatever means a diskette is formatted at the wrong density, the result is magnetically unstable with a risk of long-term data loss.

The situation was even more complex with 5¼" diskettes. The head of a 1.2M drive is narrower than that of a 360K drive, but will format, read and write 360K diskettes with apparent success. A blank 360K disk formatted and written on a 1.2M drive can be taken to a 360K drive without problems, similarly a disk formatted on a 360K drive can then be used on a 1.2M drive. However, a disk written on a 360K drive and then updated on a 1.2M drive then becomes permanently unreadable on any 360K drive, owing to the incompatibility of the track widths. There are several other scenarios that will not work.

Useless floppy disk trivia - the write-protect and high-density holes on a 3½" disk are spaced exactly as far apart as the holes in punched A4 paper, allowing (write protected) floppies to be clipped into European ringbinders[?].



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