Abstract: A disk drive has a normal mode of operation and a built-in self-test (BIST) mode of operation for producing a sequence of channel metrics {&Ggr;n}. The disk drive includes a recording surface having a plurality of bit cells and a transducer for reading the plurality of bit cells to produce a noise-corrupted read signal. The disk drive further includes means responsive to the noise-corrupted read signal for generating a sequence of observed samples {yn}, the sequence of observed samples {yn} forming a sequence of observed-sample subsequences {Yn}. An expected sample generator operates during the BIST mode of operation to provide a sequence of expected samples {wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn}. A channel metrics &Ggr;n computation system computes a sequence of channel metrics {&Ggr;n}.

Abstract: A storage system employs a method for encoding a sequence of input data blocks into a sequence of codewords. Each input data block includes a first predetermined number of bits (the data block length). Each codeword includes a second predetermined number of bits (the codeword length). The code rate, i.e., the ratio of the first number to the second number, is greater than ¾. The method is performed in a sampled-data channel in a storage system; and the channel includes a circuit the performance of which is adversely affected by an excessive run length of bits between occurrences of a predetermined influential pattern. Preferably, the influential pattern is a two-bit sequence of adjacent 1's, which favorably influences the performance of a timing recovery circuit. The method includes receiving the sequence of input data blocks and generating the sequence of codewords responsive to the received sequence of input data blocks.

Abstract: In a hard disk drive, a semiconductor chip includes a circuit used in a built-in self test (“BIST”) to determine an amplitude of a dibit echo for characterizing nonlinear distortion of a readback signal. Preferably, write precompensation is performed based on results of the BIST to minimize distortion attributable to intersymbol interference. A generator is used to generate a maximal length pseudo-random sequence. This maximal length pseudo-random sequence is input to a correlator which performs a correlation between the maximal length pseudo-random bit sequence and a readback signal responsive to the pseudo-random sequence that was stored onto a disk of the hard disk drive. In one embodiment, a seed value stored in memory is loaded into the generator upon detection of a synchronization signal read from the disk. With the appropriate seed value loaded into the generator, a specific pseudo-random bit sequence corresponding to a sample point of interest is then generated.

Abstract: A partial-response maximum-likelihood (PRML) sequence detector with decision feedback equalization (DFE) for a disk drive read channel. The symbol recovery method for a disk drive read channel produces a sequence of samples X.sub.n of a magnetic readback signal with amplitudes representing the readback signal during corresponding sample intervals n=1-N. A DFE circuit generates a sequence of equalized samples y.sub.n and includes a feed-forward filter that removes precursor ISI from the sequence of sample signals x.sub.n to produce a sequence of feed-forward equalized samples w.sub.n, detection logic that translates the sequence of equalized samples y.sub.n into a sequence of detected symbols y.sub.n, and a feedback filter that filters the sequence of detected symbols y.sub.n to produce a sequence of equalization feedback values e.sub.n to offset postcursor ISI remaining in the sequence of feed-forward equalized samples w.sub.n. A combinational circuit receives the feed-forward equalized samples w.sub.