Double density

	Email		Print
	Bookmark		Link

Double density

Double density, often shortened DD, is a capacity designation on magnetic storage

Magnetic storage

Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory....
, usually floppy disk

Floppy disk

A floppy disk is a data storage medium that is composed of a disk of thin, flexible magnetic storage medium encased in a square or rectangle plastic shell....
s. It describes the use of an encoding (or modulation

Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
) of information

Information

Information as a Conveyed concept has a diversity of meanings, from everyday usage to technical settings. Generally speaking, the concept of information is closely related to notions of constraint, communication, control system, data, form, instruction, knowledge, Meaning , stimulation, pattern, perception, and knowledge representation....
, which can encode

Encode

Encode may refer to:* Can be related to "Code"* Encode ApS, a Danish software company* ENCODE, the ENCyclopedia Of DNA Elements...
on average twice as many bits per time unit compared to single density

Single density

Single density, often shortened SD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding of information using Frequency modulation....
. This is achieved by using MFM

Modified Frequency Modulation

Modified Frequency Modulation, commonly MFM, is a line code scheme used to encode information on most floppy disk formats, which include the floppy disk formats used in the classic versions of Amiga OS, most CP/M operating system machines as well as IBM PC compatibles running DOS....
instead of FM

Frequency modulation

In telecommunications, frequency modulation conveys information over a carrier wave by varying its frequency . In analog signal applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal....
.

Floppy disk

Floppy disk

A floppy disk is a data storage medium that is composed of a disk of thin, flexible magnetic storage medium encased in a square or rectangle plastic shell....
drives have been using this method since 1978 with the introduction of the 360 KiB (MS-DOS

MS-DOS

MS-DOS is an operating system commercialized by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s....
FAT

File Allocation Table

File Allocation Table or FAT is a computer file system architecture now widely used on most computer systems and most memory cards, such as those used with digital cameras....
size) drives.

The early hard disk

Hard disk

A hard disk drive , commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating hard disk platters with magnetic surfaces....
s also used this encoding, but was replaced by the more efficient RLL

Run Length Limited

Run length limited or RLL coding is a Line code technique that is used to send arbitrary data over a Channel with Bandwidth limits. This is used in both telecommunication and storage systems which move a medium past a fixed head....
method.

de:Double Density