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== Implementation in Products ==
[[File:PRML chronology circa 1994 (scanned Nov 1, 2019).pdf|thumb|Early PRML chronology (created around 1994)]]
The first two implementations were in Tape (Ampex - 1984) and then in hard disk drives (IBM - 1990). Both are significant milestones with the [[Ampex]] implementation focused on very high data-rate for a digital instrumentation recorder and [[IBM]] focused on a high level of integration and low power consumption for a mass-market HDD. In both cases, the initial equalization to PR4 response was done with analog circuitry but the Viterbi algorithm was performed with digital logic. In the tape application, PRML superseded 'flat equalization'. In the HDD application, PRML superseded [[run-length limited|RLL]] codes with 'peak detection'.
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