Floppy disk
From ECDL.web
A floppy disk is a data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium sealed in a square or rectangular plastic carrier lined with fabric that removes dust particles. 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 three decades as a popular and ubiquitous form of data storage and exchange, from the mid-1970s well into the 2000s. 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disk drives still have some limited uses, especially with legacy industrial computer equipment, they have now been superseded by USB flash drives, external hard disk drives, optical discs, memory cards and computer networks.
Operation
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.
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.
Usage
The flexible magnetic 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, in addition to application software and data. Most home computers had a primary operating system 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. 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. 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.
Disk formats
Floppy physical sizes are often referred to by the nominal size in inches, even in countries where metric is the standard. Formatted capacities are generally set in terms of kilobytes (1024 bytes), written as "kB".
The earliest floppy disks, invented at IBM, were 8 inches in diameter. In 1976 Shugart Associates introduced the first 5¼-inch FDD and associated media. By 1978 there were more than 10 manufacturers producing 5¼-inch FDDs, in competing disk formats. In 1984, IBM introduced the 1.2 megabyte dual sided floppy disk along with its AT model. Although often used as backup storage, the high density floppy was not often used by software manufacturers for interchangeability. In 1986, IBM began to use the 720 kB double density 3.5" microfloppy disk on its Convertible laptop computer. It introduced the so-called "1.44 MB" high density version with the PS/2 line. These disk drives could be added to existing older model PCs.
Throughout the early 1980s the limitations of the 5¼-inch format were starting to become clear. Originally designed to be smaller and more practical than the 8-inch format, the 5¼-inch system was itself too large, and as the quality of the recording media grew, the same amount of data could be placed on a smaller surface. 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. By the mid-1990s the 5¼-inch drives had virtually disappeared as the 3½-inch disk became the predominant floppy disk. One of the chief advantages of the 3½-inch disk, besides its smaller size which allows it to fit in a shirt pocket, is its plastic case, which gives it better protection from dust, liquids, fingerprints, scratches, sunlight, warping, and other environmental risks.