Floppy Disk – What is it?
Floppy disks are read and written by a floppy disk drive or FDD, Invented by the American information technology company IBM, floppy disks in 8 inch, 5¼ inch and 3½ inch forms enjoyed nearly three decades as a popular and ubiquitous form of data storage and exchange, from the mid-1970s to the late 1990s. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have now been superseded by USB flash drives, external hard disk drives, optical discs, memory cards and computer networks.
A small motor in the drive rotates the diskette at a regulated speed, while a second motor-operated mechanism moves the magnetic read–write head,(or heads, if a double-sided drive) along the surface of the disk. Both read and write operations require physically contacting the read–write head to the disk media, an action accomplished by a "disk load" solenoid. To write data onto the disk, current is sent through a coil in the head. The magnetic field of the coil magnetizes spots on the disk as it rotates; the change in magnetization encodes the digital data. To read data, the tiny voltages induced in the head coil by the magnetization on the disk are detected, amplified by the disk drive electronics, and sent to the Floppy disk controller. The controller separates the data from the stream of pulses coming from the drive, decodes the data, tests for errors, and sends the data on to the host computer system.
A blank diskette has a uniform featureless coating of magnetic oxide on it. A pattern of magnetized tracks, each broken up into sectors, is initially written to the diskette so that the diskette controller can find data on the disk. The tracks are concentric rings around the diskette, with spaces between the tracks where no data is written. Other gaps, where no user data is written, are provided between the sectors and at the end of the track to allow for slight speed variations in the disk drive. These gaps are filled with padding bytes that are discarded by the diskette controller. Each sector of data has a header that identifies the sector location on disk. An error checking cyclic redundancy check is written into the sector headers and at the end of the user data so that the diskette controller can detect errors when reading the data. Some errors (soft errors) can be handled by re-trying the read operation. Other errors are permanent and the disk controller will signal failure to the operating system if multiple tries cannot recover the data.
Formatting a blank diskette is usually done by a utility program supplied by the computer operating system manufacturer. Generally the disk formatting utility will also set up an empty file storage directory system on the diskette, as well as initializing the sectors and tracks on a blank diskette. Areas of the diskette that can't be used for storage due to some flaw can be locked out so that the operating system does not attempt to use the "bad sectors". This could be quite time consuming, so many environments had an option to "quick format" which would skip the error checking process. During the heyday of diskette usage, diskettes pre-formatted for popular computers were sold.
The flexible magnetic disk, commonly called floppy disk, revolutionized computer disk storage for small systems and became ubiquitous in the 1980s and 1990s in their use with personal computers and home computers to distribute software, transfer data, and create backups.
Before hard disks became affordable, floppy disks were often also used to store a computer's operating system (OS), in addition to application software and data. Most home computers had a primary OS (and often BASIC) stored permanently in on-board ROM, with the option of loading a more advanced disk operating system from 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 demanded multiple diskettes; a large package like Windows or Adobe Photoshop could use a dozen disks or more. By 1996, there were an estimated five billion floppy disks in use. Throughout the 1990s, distribution of larger packages was gradually switched to CD-ROM (or online distribution for smaller programs).
Mechanically incompatible higher-density media were introduced (e.g. the Iomega Zip disk) and were briefly popular, but adoption was limited by the competition between proprietary formats, and the need to buy expensive drives for computers where the media would be used. In some cases, such as with the Zip drive, the failure in market penetration was exacerbated by the release of newer higher-capacity versions of the drive and media that were not backward compatible with the original drives, thus fragmenting the user base between new users and early adopters who were unwilling to pay for an upgrade so soon. A chicken or the egg scenario ensued, with consumers wary of making costly investments into unproven and rapidly changing technologies, with the result that none of the technologies were able to prove themselves and stabilize their market presence. Soon, inexpensive recordable CDs with even greater capacity, which were also compatible with an existing infrastructure of CD-ROM drives, made the new floppy technologies redundant. The last advantage of floppy disks, reusability, was diminished by the extremely low cost of CD-R media, and finally countered by re-writable CDs. Later, pervasive networking, as well as advancements in flash-based devices and widespread adoption of the USB interface provided another alternative that, in turn, made even optical storage obsolete for some purposes.
An attempt to continue the traditional diskette was the SuperDisk (LS-120) in the late 1990s, with a capacity of 120 MB, which was backward compatible with standard 3½-inch floppies. For some time, PC manufacturers were reluctant to remove the floppy drive because many IT departments appreciated a built-in file-transfer mechanism (dubbed Sneakernet) that always worked and required no device driver to operate properly. However, manufacturers and retailers have progressively reduced the availability of computers fitted with floppy drives and of the disks themselves. Widespread built-in operating system support for USB flash drives, and even BIOS boot support for such devices on most modern systems, has helped this process along.
Imation USB floppy drive, model 01946. An external drive that accepts high-density disks.
External USB-based floppy disk drives are available for computers that support USB mass storage devices. Many modern systems provide firmware support for booting to a USB-mounted floppy drive.
Floppy physical sizes are often referred to by the nominal size in inches, even in countries where metric is the standard, and even though the size is defined in metric. For example, the ANSI specification is entitled in part "90-mm (3.5-in)", even though 90 mm is more nearly 3.54 inches. Formatted capacities are generally set in terms of kilobytes (1024 bytes), written as "kB".
