code (Modified Frequency Modulation code) A method of encoding analog signals into magnetic bits or optical pits. MFM uses a fixed length encoding scheme that eliminates the need for space-consuming timing information used in FM. Bits are evenly spaced in time on the disk surface. This type of encoding scheme allows even single bit errors to be detected and corrected by the controller electronics. MFM was eventually replaced by the RLL method in hard drives, but it is still used in floppy drives.