Floppy disk format and density refer to the logical and physical layout of data stored on a
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined ...
. Since their introduction, there have been many popular and rare floppy disk types, densities, and formats used in computing, leading to much confusion over their differences. In the early 2000s, most floppy disk types and formats became obsolete, leaving the -inch disk, using an
IBM PC
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a tea ...
compatible format of 1440 KB, as the only remaining popular format.
Different floppy disk types had different recording characteristics, with varying magnetic
coercivity
Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercivity is usually measured in ...
(measured in
oersted
The oersted (symbol Oe) is the coherence (units of measurement), coherent derived unit of the Magnetic field#The H-field, auxiliary magnetic field H in the centimetre–gram–second system of units (CGS). It is equivalent to 1 dyne per maxwell ...
s, or in modern
SI units in
ampere
The ampere (, ; symbol: A), often Clipping (morphology), shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One amp ...
s per meter), ferrite grain size, and tracks per inch (TPI). TPI was not a part of the physical manufacturing process; it was a certification of how closely
track
Track or Tracks may refer to:
Routes or imprints
* Ancient trackway, any track or trail whose origin is lost in antiquity
* Animal track, imprints left on surfaces that an animal walks across
* Desire path, a line worn by people taking the short ...
s of data could be spaced on the medium safely.
The term density has a double meaning for floppy disks. Originally, single density and double density indicated a difference in logical encoding on the same type of physical media:
FM for single, and
MFM for double. Subsequent use of the term "density" referred to physical ch