Floppy disk
A floppy disk, diskette, or floppy diskette is a type of disk storage made from a thin, flexible disk coated with a magnetic storage medium. It is enclosed in a square or nearly square plastic shell lined with fabric to help remove dust from the spinning disk. Floppy disks store digital data, which can be read or written when inserted into a floppy disk drive connected to or built into a computer or other device. The three most popular formats of floppy disks are the 8-inch, 5¼-inch, and 3½-inch versions.
The first floppy disks, invented and made by IBM in 1971, had a disk diameter of. Subsequently, the 5¼-inch and then the 3½-inch became a ubiquitous form of data storage and transfer into the first years of the 21st century. By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks. During this time, PCs frequently came equipped with drives of both sizes. By the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant format. The advantages of the 3½-inch disk were its higher capacity, its smaller physical size, and its rigid case which provided better protection from dirt and other environmental risks.
Floppy disks were so common in late 20th-century culture that many electronic and software programs continue to use save icons that look like floppy disks well into the 21st century, as a form of skeuomorphic design. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have been superseded by data storage methods with much greater data storage capacity and data transfer speed, such as USB flash drives, memory cards, optical discs, and storage available through local computer networks and cloud storage.
Categories
Industry observers categorize floppy disks and floppy disk drives according to size and capacity with four major categories being 8-inch, 5¼-inch, 3½-inch and high-capacity floppy disks and floppy disk drives.There were in addition variant products that did not fit these categories. The distinguishing characteristic between the high-capacity products and their lower capacity brethren, frequently categorized as standard floppies was the use of servomechanisms to increase the number of tracks and thereby increase capacity.
The four categories each represented generations, from the beginning each generation had substantially greater market success from the previous and it ultimately succeeded the previous one, but the high-capacity floppy generation although having some success was never as successful as the prior 3½-inch generation and become essentially obsolete by 2011
While the original IBM 8-inch disk was actually so defined, the other sizes are defined in the metric system, their usual names being but rough approximations.
Different sizes of floppy disks are mechanically incompatible, and disks can fit only one size of drive. Drive assemblies with both 3½-inch and 5¼-inch slots were available during the transition period between the sizes, but they contained two separate drive mechanisms. In addition, there are many subtle, usually software-driven incompatibilities between the two. 5¼-inch disks formatted for use with Apple II computers would be unreadable and treated as unformatted on a Commodore, As computer platforms began to form, attempts were made at interchangeability. Apple's later 1.44 MB high-density 3½-inch drives could read, write, and format IBM PC–compatible floppy disks. However, few IBM-compatible computers were able to read or write Apple-formatted floppy disks. The limitation was due not to the 3½-inch drive mechanism itself, but to the disk controller and its lack of support for Apple's GCR encoding used on 400 kB and 800 kB Macintosh disks.
8-inch, 5¼-inch and 3½-inch drives were manufactured in a variety of sizes, most to fit standardized drive bays. Alongside the common disk sizes were non-classical sizes for specialized systems.
History
8-inch
The first commercial floppy disks, developed in the late 1960s, were in diameter; they became commercially available in 1971 as a component of IBM products and both drives and disks were then sold separately starting in 1972 by Memorex and others. These disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation. The term "floppy disk" appeared in print as early as 1970, and although IBM announced its first media as the Type 1 Diskette in 1973, the industry continued to use the terms "floppy disk" or "floppy".Floppy disks of the first standard are 8 inches in diameter, protected by a flexible plastic jacket. It was a read-only device used by IBM as a way of loading microcode. Read/write floppy disks and their drives became available in 1972, but it was IBM's 1973 introduction of the 3740 data entry system that began the establishment of floppy disks, called by IBM the Diskette 1, as an industry standard for information interchange. Diskettes formatted for this system stored 242,944 bytes. Early microcomputers used for engineering, business, or word processing often used one or more 8-inch disk drives for removable storage; the CP/M operating system was developed for microcomputers with 8-inch drives.
The family of 8-inch disks and drives increased over time and later versions could store up to 1.2 MB; many microcomputer applications did not need that much capacity on one disk, so a smaller size disk with lower-cost media and drives was feasible. The 5¼-inch drive succeeded the 8-inch size in many applications, and developed to the same storage capacity as the larger 8-inch size, using higher-density media and recording techniques.
5¼-inch
In 1976, Shugart Associates introduced the 5¼-inch floppy disk drive. By 1978, there were more than ten manufacturers producing such drives. There were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as differential Manchester encoding, modified frequency modulation, M2FM and group coded recording. The 5¼-inch format displaced the 8-inch one for most uses, and the hard-sectored disk format disappeared. The most common capacity of the 5¼-inch format in DOS-based PCs was 360 KB for the Double-Sided Double-Density format using MFM encoding.In 1984, IBM introduced its PC/AT with the 1.2 MB dual-sided 5¼-inch floppy disk, but it never became very popular. IBM started using the 720 KB double density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and the 1.44 MB high-density version with the IBM Personal System/2 line in 1987. These disk drives could be added to older PC models. In 1988, Y-E Data introduced a drive for 2.88 MB Double-Sided Extended-Density diskettes which was used by IBM in its top-of-the-line PS/2 and some RS/6000 models and in the second-generation NeXTcube and NeXTstation; however, this format had limited market success due to lack of standards and movement to 1.44 MB drives.
Throughout the early 1980s, limits of the 5¼-inch format became clear. Originally designed to be more practical than the 8-inch format, it was becoming considered too large; as the quality of recording media grew, data could be stored in a smaller area. Several solutions were developed, with drives at 2-, 2½-, 3-, 3¼-, 3½- and 4-inches offered by various companies. They all had several advantages over the old format, including a rigid case with a sliding metal shutter over the head slot, which helped protect the delicate magnetic medium from dust and damage, and a sliding write protection tab, which was far more convenient than the adhesive tabs used with earlier disks. The established market for the 5¼-inch format made it difficult for these mutually incompatible new formats to gain significant market share. A variant on the Sony design, introduced in 1983 by many manufacturers, was then rapidly adopted. By 1988, the 3½-inch was outselling the 5¼-inch.
The head gap of an 80‑track high-density 5¼‑inch drive is smaller than that of a 40‑track double-density drive but can also format, read and write 40‑track disks provided the controller supports double stepping or has a switch to do so. A blank 40‑track disk formatted and written on an 80‑track drive can be taken to its native drive without problems, and a disk formatted on a 40‑track drive can be used on an 80‑track drive. Disks written on a 40‑track drive and then updated on an 80 track drive become unreadable on any 40‑track drives due to track width incompatibility.
Single-sided disks were coated on both sides. The reason usually given for the higher price was that double sided disks were certified error-free on both sides of the media. Double-sided disks could be used in some drives for single-sided disks, as long as an index signal was not needed. This was done one side at a time, by turning them over ; more expensive dual-head drives which could read both sides without turning over were later produced, and eventually became used universally.
3½-inch
In the early 1980s, many manufacturers introduced smaller floppy drives and media in various formats. A consortium of 21 companies eventually settled on a 3½-inch design known as the Micro diskette, Micro disk, or Micro floppy, similar to a Sony design but improved to support both single-sided and double-sided media, with formatted capacities generally of 360 KB and 720 KB respectively. Single-sided drives of the consortium design first shipped in 1983, and double-sided in 1984. The double-sided, high-density 1.44 MB disk drive, which would become the most popular, first shipped in 1986. The first Macintosh computers used single-sided 3½-inch floppy disks, but with 400 KB formatted capacity. These were followed in 1986 by double-sided 800 KB floppies. The higher capacity was achieved at the same recording density by varying the disk-rotation speed with head position so that the linear speed of the disk was closer to constant. Later Macs could also read and write 1.44 MB HD disks in PC format with fixed rotation speed. Higher capacities were similarly achieved by Acorn's RISC OS and AmigaOS.Most 3½-inch disks have a rectangular hole in one corner which, if obstructed, write-enables the disk. A sliding detented piece can be moved to block or reveal the part of the rectangular hole that is sensed by the drive. The HD 1.44 MB disks have a second, unobstructed hole in the opposite corner that identifies them as being of that capacity.
In IBM-compatible PCs, higher-density 3½-inch floppy drives can read lower-density media, but writing and formatting across densities has reliability issues and was not officially supported by manufacturers. Writing at different densities than those at which disks were intended, sometimes by altering the density detection hole, was possible but not supported by manufacturers. A hole on one side of a 3½-inch disk can be altered to make some disk drives and operating systems treat the disk as one of higher or lower density, for bidirectional compatibility or economic reasons. Some computers, such as the PS/2 and Acorn Archimedes, ignored these holes altogether.
Generally, the term floppy disk persisted, even though later style floppy disks have a rigid case around an internal floppy disk.