V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MFM
       Modified Frequency Modulation


The Free On-line Dictionary of Computing (30 December 2018):

Modified Frequency Modulation
MFM

    (MFM, Modified FM, or sometimes "Multiple
   Frequency Modulation") A modification to the original
   frequency modulation scheme for encoding data on magnetic
   disks.  MFM allows more than 1 symbol per flux transition (up
   to 3), giving greater density of data.  It is used with a data
   rate of between 250-500 kbit/s on industry standard 3.5" and
   5.25" low and high density diskettes, and up to 5 Mbit/s on
   ST-506 hard disks.  Except for 1.44 MB floppy disks, this
   encoding is obsolete.

   Other data encoding schemes include GCR, FM, RLL.  See
   also: PRML.

   (2002-06-24)