Partial Response Maximum Likelihood
<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".
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