Abstract: A sampled amplitude read channel for reading information stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values, the interpolated sample values generated by interpolating a sequence of discrete time channel sample values generated by sampling pulses in an analog read signal from a magnetic read head positioned over the magnetic medium. A write VFO generates a write clock for writing digital data to the magnetic medium at a predetermined baud rate for a selected zone, and upon read back, the write VFO generates a sampling clock at a frequency slightly higher than the write frequency. A sampling device samples the analog read signal at the sampling clock rate to generate a sequence of discrete time channel samples that are not synchronized to the baud rate. The channel samples are equalized by a discrete time equalizing filter according to a predetermined partial response (PR4, EPR4, EEPR4, etc.).

Abstract: A synchronous read channel is disclosed which samples an analog read signal from a magnetic read head positioned over a magnetic disk medium, filters the sample values according to a desired partial response, extracts timing information from the filtered sample values, and detects an estimated data sequence from the filtered sample values using a discrete time sequence detector. The read channel further employs an error tolerant sync mark detector, as well as a sync mark recovery procedure for synchronizing to the data when the sync mark is destroyed by a defect.

Abstract: A method and apparatus for calibrating an analog equalizer in a sampled amplitude read channel is disclosed wherein the filter's frequency response is measured and calibrated directly. This is accomplished by injecting a known periodic signal into the analog filter and measuring a spectrum value at a predetermined frequency. The filter parameters are adjusted accordingly until the spectrum reaches a predetermined target value. In the preferred embodiment, the analog filter comprises at least one second order low pass filter (referred to as a biquad filter), and the filter's spectrum is adjusted relative to the well known parameters f.sub.o and Q. Specifically, the parameters f.sub.o and Q are optimized relative to a power measurement at predetermined harmonics of the input signal. In this manner, the present invention enables auto-calibration of the analog equalizer without reading any data from the disc.

Abstract: A magnetic disc storage system employing two stage actuators for simultaneously positioning recording heads over the top and bottom surfaces of the disc is disclosed. The recording heads are fastened to a distal end of respective top and bottom load beams. A base end of the load beams is connected to a voice coil motor (VCM) rotary actuator which simultaneously positions both recording heads over the disc. A silicon microactuator is also fastened to the distal end of at least one of the load beams for positioning the recording heads independent of one another, thereby allowing simultaneous tracking of embedded servo data. Various data formats are provided, including interleaving logical sector numbers, symbols of a logical sector, and segments of a logical sector, between the top and bottom physical sectors of a track.

Abstract: A sampled amplitude read channel is disclosed for disk storage systems which asynchronously samples an analog read signal, adaptively equalizes the resulting discrete time sample values according to a target partial response, extracts synchronous sample values through interpolated timing recovery, and detects digital data from the synchronous sample values using a Viterbi sequence detector. To increase the speed of the read channel, the FIR filters in the equalizer and interpolator are implemented according to a residue number system. Further, the residue number system implementation of the FIR filters uses "one-hot" encoding to decrease power dissipation.

Abstract: A disc drive storage system having a plurality of data tracks and data sectors within each track, wherein each track further comprises a redundancy sector for reconstructing a data sector unrecoverable at the sector level. The latency of the storage system is minimized by generating track level redundancy data over the write range of data sectors and storing the "write" redundancy to the redundancy sector. Then during idle time of the storage system, the track level redundancy is regenerated for the entire track. If an unrecoverable data sector is encountered during the idle time redundancy regeneration, and the unrecoverable data sector is within the write range of the previous write operation, then it is reconstructed using the track level redundancy data stored in the redundancy sector.

Abstract: A synchronous read channel is disclosed which samples an analog read signal from a magnetic read head positioned over a magnetic disk medium, filters the sample values according to a desired partial response, extracts timing information from the filtered sample values, and detects an estimated data sequence from the filtered sample values using a discrete time sequence detector. To increase the throughput of the read channel, multiple sample values are processed in parallel. In the example embodiment disclosed herein, two sample values are processed in parallel.

Abstract: This invention provides apparatus for reliably and efficiently reading data from a magnetic storage medium under the condition that adjacent magnetization regions are partially erased. A simplified nonlinear description of a read signal resulting from such partially erased magnetization regions is used to derive a state machine model of the read signal. The state machine model implicitly defines a sequence detector for demodulating recorded data from received samples. For a PR4 signal, the state machine has ten states; for an EPR4 signal, the state machine has eighteen states; and for an EEPR4 signal, the state machine has twenty-six states. The PR4 machine is further simplified using squaring and state sharing to provide state machine models with six and four states.

Abstract: A discrete time servo demodulation technique incorporated within a sampled amplitude read channel to demodulate embedded servo field information stored on a magnetic medium. The servo field information is transduced by a read head into an analog signal, and converted to a sequence of sample values in the read channel. The demodulation technique is responsive to the sample values and includes a discrete time peak detector for detecting servo data, and a discrete time servo burst amplitude detector for measuring the amplitude of servo bursts. Peaks are detected in the analog read signal by sensing a change of slope from the sequence of sample values. The peaks are qualified by polarity in that a peak is detected only if its polarity is opposite in sign from the previous peak. The servo burst amplitudes are measured by interpolating, rectifying, and accumulating the sequence of sample values corresponding to the servo bursts.

Abstract: In a disc storage system employing multiple recording heads to increase throughput by providing simultaneous access through multiple data streams, a sampled amplitude read channel is disclosed for detecting, in parallel, estimated data sequences from the read signals associated with each data stream. Timing recovery in the read channel is implemented through interpolation, that is, by asynchronously sampling the analog read signals and interpolating to synchronous sample values. In this manner, a frequency synthesizer can generate a single reference clock for clocking operation of all the discrete time circuitry, thereby eliminating noise caused by multiple clocks as well as simplifying diagnostics. Furthermore, interpolated timing recovery avoids noise due to cross-talk between voltage controlled oscillators (VCOs) that would likely occur in a conventional synchronous sampling timing recovery design. A significant advantage is that the read channel can reside in a single integrated circuit.

Abstract: A sliding mode controller is disclosed for controlling a read/write head actuator in a magnetic disk drive storage system wherein a voice coil motor connected to the actuator operates to adjust the position of the read/write head over a selected data track recorded on a magnetic medium. The sliding mode controller comprises an improved technique for reducing chatter associated with the inherent operation of such a controller--rapid switching between gains to force the observable phase states to follow a predetermined phase state trajectory. The sliding mode controller generates a motor control command by multiplying an actuator position error and an actuator position error velocity by respective switching gains. The gains are switched according to a predetermined relationship .sigma. between the phase states and a phase state trajectory. In order to reduce the switching frequency (i.e.

Abstract: A synchronous read channel is disclosed which samples an analog read signal from a magnetic read head positioned over a magnetic disk medium, filters the sample values according to a desired partial response, extracts timing information from the filtered sample values, and detects an estimated data sequence from the filtered sample values using a discrete time sequence detector. The read channel employs a Data Randomizer which processes unencoded user data to insure that the channel bit patterns with worst-case pattern sensitivity occur no more frequently than would be expected from random user data. The Data Randomizer employs two linear feedback shift registers: one generates a 63-bit sequence which is EXLUSIVE-OR-ed against the MSB of each pair of data bits, the other generates a 127-bit sequence which is EXCLUSIVE-OR-ed against the LSB of each pair of data bits. The Data Randomizer does not affect error propagation.

Abstract: A magnetic disk storage system is disclosed wherein byte synchronization to sector data is achieved even when noise in the read channel, due for instance to a thermal asperity (TA), corrupts the primary preamble and/or sync mark fields or causes a loss of frequency or phase lock. The data sector format is modified to comprise at least one secondary sync mark in addition to the conventional primary sync mark recorded at the beginning of the data field. In this manner, when the primary sync mark becomes undetectable due to errors, or when byte synchronization is lost, the storage system can still synchronize to the data sector using the secondary sync mark. The secondary sync mark is preferably spaced apart from the primary sync mark with either a gap (no data) or user data inserted inbetween.

Abstract: A defect management system is disclosed for disc storage systems which avoids the access latency associated with conventional linear replacement techniques by dispersing spare segments throughout each track at a regular interval and buffering sectors inbetween a defective sector and the corresponding spare segment during read and write operations. In one embodiment, a spare segment is an entire sector which replaces a defective data sector; and in an alternative embodiment, a spare segment stores only the defective portion of a data sector which is more efficient, but also more complicated in implementation. In both embodiments, the defect management system comprises a defect locator for locating a defective segment within a data sector. Once located, the defect management system maps the defective sector (or the defective portion thereof) to the nearest available spare segment.

Abstract: A rate 16/17 ENDEC is disclosed which encodes 16 bit input data words into 17 bit codewords according to at least one predetermined code constraint, such as an RLL (d,k) constraint. The encoder encodes the high and low byte of the input data word using the same mapping circuitry which reduces its cost and complexity. The codewords are transferred through a communication channel, such as a computer disc storage device, and upon reception (or readback) the first 8 bits of the 17 bit codeword are decoded independent from the last 8 bits which prevents error propagation. That is, the first 8 bits of the codeword are decoded into a high byte of the decoded data word, and the last 8 bits of the codeword are decoded into a low byte of the decoded data word independent from one another.

Abstract: A disc storage system comprising a sector level ECS for correcting errors within a sector during readback, and a track level ECS for correcting a sector that becomes unrecoverable at the sector level either because the number of hard errors exceeds the error correction capability of the sector redundancy, or because the sector is unreadable due, for instance, to an inability to synchronize to the sector data. A data buffer stores the data sectors, and a redundancy buffer stores the track level redundancy data. If during a read operation a data sector is determined to be unrecoverable using the sector level redundancy, the storage system corrects the unrecoverable sector using the track level redundancy.

Abstract: In a storage system using multiple disk drives, the disk drive spindles are rotated at the same frequency and at a predetermined phase relationship. A phase angle, measured as the difference between an index mark recorded on the disk and the disk's read head, is used to control the spindle rotation speed. Each of the disk drives are first independently frequency locked to a target frequency, and once frequency locked, each disk drive is phase locked in relation to one another. In the phase locking process, each disk generates a synchronizing signal for synchronizing the rotation of the disks to a predetermined phase relationship. If any one of the disk drives becomes inoperable (due to a failure or "hot-swapping"), the other disk drives remain synchronized since the synchronizing signal is not lost.

Abstract: A partial response class-IV (PR4) read channel is disclosed for magnetic recording including a coding scheme which improves timing recovery by providing a more accurate phase error estimate. The conventional 1/(1+D.sup.2) precoder is not used in the present invention (to avoid the ambiguous initial state), so that the read channel can directly control the flux transitions written onto the magnetic disc. This enables the read channel to encode user data according to a criteria that creates well defined slopes in the analog read signal at the sample instances, thereby improving the accuracy of the timing recovery phase error estimate.

Abstract: A sampled amplitude read channel is disclosed for disc storage systems which asynchronously samples an analog read signal, equalizes the resulting discrete time sample values according to a target partial response, extracts synchronous sample values through interpolated timing recovery, and detects digital data from the synchronous sample values using a Viterbi sequence detector. The interpolated timing recovery comprises a zero phase restart circuit for minimizing an intial phase error between expected sample values and interpolated sample values at the beginning of an acquisition mode by computing an initial sampling phase offset.

Abstract: A sliding mode controller is disclosed for controlling the motion of a read/write head actuated by a voice coil motor over a rotating magnetic disk storage medium. The magnetic disk comprises a plurality of concentric data tracks recorded thereon wherein each data track comprises user data and servo data. The sliding mode controller operates by multiplying a head position error phase state and a head position error velocity phase state by respective switching gains to force the phase states to follow a predetermined phase state trajectory. The phase state trajectory can be defined by a single linear segment, a variable linear segment, multiple linear segments over the entire region of excursion, or optimum parabolic acceleration and deceleration segments. Switching logic, responsive to the phase states and a trajectory segment value .sigma., switches between positive and negative feedback gains to drive the phase states toward a current trajectory segment. A .sigma.