mfm

from The Free On-line Dictionary of Computing (8 July 2008)
Modified Frequency Modulation
MFM

   <storage> (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   encoding is obsolete.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)