Recording techniques fm, mfm and rll

Recording techniques

Frequency modulation(FM) encoding technique

1. This method of data encoding is also known as the “Single density recording”. 
2. In FM format a clock pulse is given at beginning to each bit cell. The data pulse is given at center of each bit cell.
3. In this FM method of data recording a 1 bit is stored as two pulses(one clock pulse and one data pulse), and a o bit is stored as a one pulse and one gap or no pulse. 

Modified frequency modulation encoding technique

1. In MFM technique, the data pulse is given at beginning of each bit cell.
2. When the data is 1, there is no clock pulse, only data pulse is given at the center of bit cell.
3. When the data is 0, there is a 1 in a previous bit cell, neither clock pulse nor data pulse is written.