MFM encoding - Revision history

Kyz: /* Floppy disk formats using MFM encoding */

2016-12-10T14:24:20Z

‎Floppy disk formats using MFM encoding

Dan Tobias: /* Floppy disk formats using MFM encoding */

2013-05-05T04:21:10Z

‎Floppy disk formats using MFM encoding

Dan Tobias: Created page with "{{FormatInfo |formattype=physical |subcat=Floppy disk |released=1970 }} '''MFM encoding''' (Modified Frequency Modulation) is, as its name implies, a modified version of [[FM..."

2013-05-05T04:11:47Z

Created page with "{{FormatInfo |formattype=physical |subcat=Floppy disk |released=1970 }} '''MFM encoding''' (Modified Frequency Modulation) is, as its name implies, a modified version of [[FM..."

New page

{{FormatInfo
|formattype=physical
|subcat=Floppy disk
|released=1970
}}

'''MFM encoding''' (Modified Frequency Modulation) is, as its name implies, a modified version of [[FM encoding]]. It was originally developed for use in early IBM [[hard disk]]s (where it was used starting in 1970), but became most notable for its widespread use in [[floppy disk]]s, including the standard PC/MS-DOS formats and most CP/M formats as well as some others.

Similarly to FM, MFM encoding depends on changes of signal rather than absolute magnitude, but it uses a more compact scheme for representing data bits. FM encoding required two transitions for some bits, while MFM uses only one transition per bit at most, zero for some bits, though extra "clock bits" and "sync marks" are also added. Elaborate rules for the placement of all these signals are needed to prevent multiple zero bits encoded with no transitions appearing in a row, since it is rather hard to count the number of consecutive occurrences of the absence of a signal transition.

== Floppy disk formats using MFM encoding ==
* [[IBM Type 2D]]

== Links ==
* [[Wikipedia:Modified Frequency Modulation|Wikipedia article]]

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 * [[Acorn double density 5 1/4" disk]]
 * [[Acorn high density 3 1/2" disk]]
 * [[Apple double-density 3 1/2" disk]]
 * [[Commodore 1581 disk]]

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 == Floppy disk formats using MFM encoding ==
 * [[IBM Type 2D]]
 == Links ==
 * [[Wikipedia:Modified Frequency Modulation|Wikipedia article]]