Modified Modified Frequency Modulation (MMFM or M2FM) is a further development of Modified Frequency Modulation(MFM) with an improved algorithm that suppresses additional clock bits and thus increases the Run Length Limited( RLL).
In this method, a clock pulse is inserted between two consecutive zeros only if no clock pulse was inserted at the first bit of the bit pair. With the MMFM method, the synchronization marks are produced by an additional clock pulse. This is inserted between consecutive zeros between which it would normally be missing. For example, a clock pulse is inserted in the middle of the bit combination 10001.