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== Modern electronics ==
Although the PRML acronym is still occasionally used, advanced detectors are more complex PRML operate at higher data-rates. The analog front-end typically includes [[Automatic_gain_control|AGC]], correction for the nonlinear read-element response, and a low-pass filter with control over the high-frequency boost or cut. Equalization is done after the ADC with a digital [[FIR filter]]. ([[Two-dimensional magnetic recording|TDMR]] uses a 2-input, 1-output equalizer.) The detector uses the PDNP/NPML approach but the hard-decision Viterbi algorithm is replaced with a detector providing soft-outputs (additional information about the reliability of each bit). Such detectors using a soft Viterbi algorithm or [[BCJR algorithm]] are essential in iteratively decoding the [[low-density parity-check code]] used in modern HDDs. A single integrated circuit contains the entire read and write channels (including the iterative decoder) as well as all the disk control and interface functions. There are currently two suppliers: [[Broadcom]] and [[Marvell Technology Group|Marvell]].<ref>{{cite web |url=https://www.marvell.com/storage/assets/Marvell_88i9422_Soleil_pb_FINAL.pdf |title=Marvell 88i9422 Soleil SATA HDD Controller |date=September 2015}}{{dead link|{{subst:DATE}}|date=April 2020}}</ref>
== See also ==
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