Partial Response Maximum Likelihood definition storage
(PRML) A method for converting the weak analog
signal from the head of a magnetic disk
drive into a digital signal. PRML attempts to correctly interpret even small changes in the analog signal, whereas peak detection relies on fixed thresholds. Because PRML can correctly decode a weaker signal it allows higher density recording.
For example, PRML would read the magnetic flux density pattern 70, 60, 55, 60, 70 as binary "101", and the same for 45, 40, 30, 40, 45. A peak detector would decode everything above, say, 50 as high, and below 50 as low, so the first pattern would read "111" and the second as "000".