Abstract: A write channel includes a pre-encoding module that encodes write data to produce pre-encoded data. An error correcting code (ECC) module generates ECC data based on the pre-encoded data. A post-encoding module encodes the ECC data to produce post-encoded data. A combining module combines the pre-encoded data and the post-encoded data for writing to the storage medium.

Abstract: A technique to detect defects when reading a defect scan pattern stored on a disk in which the detected defects are processed differently depending on which region of a sector the defect is resident. In one implementation, a mask is used to identify the defects of different regions. By differentiating different regions within the sector for defect scan, sync mark and preamble fields may be treated as critical regions so that different defect scan properties may be attributed when performing the defect scan.

Abstract: A write channel includes a pre-encoding module that encodes write data to produce pre-encoded data. An error correcting code (ECC) module generates ECC data based on the pre-encoded data. A post-encoding module encodes the ECC data to produce post-encoded data. A combining module combines the pre-encoded data and the post-encoded data for writing to the storage medium.

Abstract: A defect detector a hard disk drive includes a signal energy processor that produces at least one energy signal from a plurality of read samples. A comparator module compares the at least one energy signal to at least one corresponding energy threshold and generates defect data when the at least one energy signal compares unfavorably to the at least one corresponding energy threshold.

Abstract: Automatically optimizing and programming features of a disk drive read channel for a selected partial response (PR) target. This enables flexible PR targets to be used in the read channel. The flexible PR targets can have arbitrary coefficients, and the channel features (parameters, functions and algorithms) that are dependent on the flexible PR targets are automatically adapted and programmed in hardware or firmware. With flexible PR targets, the read channel can support longitudinal and perpendicular recording without compromising performance.

Abstract: A method for detecting signals affected by intersymbol interference provides for a path memory in the form of a trellis admitting survivor paths comprising a first and a second stage. The first stage includes a shift register exchange with a given number of states and a given length ?. The first stage outputs a first state SAkk-? on the survivor path for the best state Ak, and a second state SBkk-? on the survivor path for another state Bk. The second stage is configured as a two-state shift register exchange having a respective memory length ?, including respective first and second registers. In the respective first and second registers the survivor paths are stored leading to a respective first ?0k and second ?1k state, whereby the respective first register contains the backend of the best survivor path, while the respective second register contains the backend of an alternative survivor path.

Abstract: Multiple levels of guided scrambling. Selective scrambling is performed on user data (or any information) that is to be output. The selection of which scrambling is to be employed can be based on whether or not a baseline error constraint and/or randomness constraint is met. The writing of the scrambled user data can be performed in parallel with, during the same time period, and/or simultaneously with the determination of whether or not a baseline error constraint and/or randomness constraint is met. If the constraint is not met, the outputting and/or writing of the scrambled user data can be aborted mid-process.

Abstract: A technique to detect head instability by monitoring for a baseline popping (BLP) noise effect on demodulation bursts read from a disk. In one technique, a digital filter is employed as a moving average filter so that the filtering of the bursts has a zero output from the filter if only the bursts are present. However, when a BLP event occurs, the noise effect causes a non-zero output from the filter. A threshold value is set and when the output of the filter exceeds the threshold value, a BLP indication is noted. Although various filters may be used, in one technique, a filter suitable for use in detecting thermal asperity defects is used for the BLP detection filter.

Abstract: A technique to detect defects when reading a defect scan pattern stored on a disk in which the detected defects are processed differently depending on which region of a sector the defect is resident. In one implementation, a mask is used to identify the defects of different regions. By differentiating different regions within the sector for defect scan, sync mark and preamble fields may be treated as critical regions so that different defect scan properties may be attributed when performing the defect scan.

Abstract: A media noise optimized (MNO) detector for a read channel compensates for pattern dependent media noise, and compensates for nonlinearities from many sources such as residual MR nonlinearity, residual nonlinear transition shift, partial erasure, write-induced nonlinearity, and steady-state mis-equalization. The MNO detector is implemented by adjusting a conventional Viterbi detector branch metric so that the channel output value (ideal value) can be a nonlinear function of the state/branch bits, and the branch metric scaling factor is a function of the state/branch. For a given state/branch, the ideal value is the mean of analog-to-digital converter samples for the pattern corresponding to the state/branch, and the branch metric scaling factor is proportional to the noise variance for the pattern corresponding to that state/branch.

Abstract: A method for detecting signals affected by intersymbol interference provides for a path memory being arranged in the form of a trellis admitting survivor paths comprising a first and a second stage. The first stage includes a shift register exchange with a given number of states and a given length ?. At time k-?, where ? is said given length, the first stage outputs a) a first state SAkk-? on the survivor path for the best state Ak at time k, while keeping track of the parity for the state at time k-? for each of the survivor paths in said path memory, and b) a second state SBkk-? on the survivor path for another state Bk having the same intersymbol interference state as said best state Ak and the opposite priority state. The second stage as is a two-state shift register exchange having a respective memory length ?, including respective first and second registers.

Abstract: A discrete-time filtering method for identifying defects in a magnetic medium, comprising the steps of: reading data signals from at least a portion of the medium; sampling the data signals to generate discrete time sample data; processing the sample data in a discrete time filter to detect deviation of the signal corresponding to media defects; and comparing the deviation of the signal to one or more threshold values to identify corresponding defect types on the recording medium. The filter can be configured to have an impulse response substantially matched to deviation of the signal corresponding to media defects.

Abstract: A method and apparatus for encoding a sequence of 32 bit digital data words into a sequence of 33 bit code words in consonance with predetermined minimum zero run length (d) and predetermined maximum zero run length (k) for recording upon a magnetic medium within a magnetic recording channel is disclosed. The method comprises steps of dividing each data word into eight data nibbles, determining whether any data nibble contains all zeros. If no code violation, mapping the eight data nibbles to seven code nibbles and to four bits of a five bit code sub-word and setting a fifth control bit to one. If one or more code violations are present, embedding code violation locations within at least the five bit code sub-word and other code nibbles if necessary and remapping data nibbles ordinarily directed to the code sub-word and nibble locations to code locations otherwise containing the data nibbles determined to be code violations.