Partial-response maximum-likelihood

In <a href="/facts/Computer_data_storage/wPHKFpdx">computer data storage</a>, partial-response maximum-likelihood (PRML) is a method for recovering the <a href="/facts/Digital_signal_(electronics)/pKYKbxfK">digital data</a> from the weak analog read-back signal picked up by the <a href="/facts/Disk_read-and-write_head/WdpxUpjK">head</a> of a magnetic <a href="/facts/Hard_disk_drive/kekLSGSE">disk drive</a> or <a href="/facts/Tape_drive/9MfLuCa0">tape drive</a>. PRML was introduced to recover data more reliably or at a greater <a href="/facts/Areal_density_(computer_storage)/FCqKjVdU">areal-density</a> than earlier simpler schemes such as peak-detection. These advances are important because most of the digital data in the world is stored using <a href="/facts/Magnetic_storage/QaK6oArm">magnetic storage</a> on <a href="/facts/Hard_disk_drive/kekLSGSE">hard disk</a> or <a href="/facts/Tape_drive/9MfLuCa0">tape drives</a>.
Ampex introduced PRML in a tape drive in 1984. IBM introduced PRML in a disk drive in 1990 and also coined the acronym PRML. Many advances have taken place since the initial introduction. Recent <a href="/facts/Read%2fwrite_channel/WQTE8Jas">read/write channels</a> operate at much higher data-rates, are fully adaptive, and, in particular, include the ability to handle nonlinear signal distortion and non-stationary, colored, data-dependent noise (<a href="/facts/Noise-predictive_maximum-likelihood_detection/bPmJnhPm">PDNP or NPML</a>).
Partial response refers to the fact that part of the response to an individual bit may occur at one sample instant while other parts fall in other sample instants. Maximum-likelihood refers to the detector finding the bit-pattern most likely to have been responsible for the read-back waveform.

Partial-response maximum-likelihood open-in-new

Partial-response maximum-likelihood