PRML

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In computer data storage, Partial Response Maximum Likelihood (PRML) is a method for converting the weak analog signal from the head of a magnetic disk or tape 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 whereas 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".

[edit] See also

• Maximum likelihood
• Viterbi algorithm
• Extended PRML

[edit] External links

• Storage Review: PRML
• Online Chapter "Introduction to PRML" from Alex Taratorin's book "Characterization of Magnetic Recording Systems: A Practical Approach"

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.