Modified Frequency Modulation
(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 Except for 1.44 MB floppy disks, this encoding is obsolete.