Abstract: A shift code that consists of N-symbol code words is provided as an L-symbol “master sequence” in which no sub-sequence of N symbols repeats, where L?SN and S is the number of code symbols. A decoder determines a location in the code from N decoded symbols. The code locations may, for example, correspond to radial positions, or other position, times, and so forth. In one embodiment, the master sequence is continuously written to a data storage disk during a spiral write operation and a reader on a given circular track reads at least N symbols from the portion of the spiral that crosses the track and determines a code word. The radial position of the reader is then determined based on the location of the code word in the code.

Abstract: A method of forming servo data, and a self-servo write method using the same, the method including partial response maximum likelihood (PRML)-coding servo data into m bits in n-bit units; multiplying each bit of the PRML-coded result by an o multiple; and converting a bitsream obtained in the multiplying to ((m/n)?p) bits in m/n-bit units.

Abstract: A novel means for performing dibit extraction is presented. Any one of an unequalized signal dibit, equalized signal dibit, or noise dibit can be extracted. Instead of using the correlation properties of a PN (Pseudo-Noise) sequence to approximate a PN deconvolution sequence, the use of the actual deconvolution sequence (i.e., PN sequence that includes values of +k and 0, where k is oftentimes 1) is employed so that no approximations are needed. The resulting estimate of the channel is therefore very accurate.

Abstract: Systems and methods for encoding/decoding are provided. The systems and methods include encoding a stream of K-bit input sequences into a stream of (G, I, M)-constrained 2N-bit output sequences by transforming each K-bit input bit sequence into two separate data paths including even and odd bits. Enumerative maximum-transition-run (eMTR) encoding of the even bits generates constrained even bits, and enumerative maximum-transition-run (MTR) encoding of the odd bits generates constrained odd bits. The constrained even and constrained odd bits are interleaved to form a stream of (G, I, M)-constrained 2N-bit output sequences where G is a global constraint, I is an interleave constraint, and M is a variable frequency oscillator constraint of a partial-response maximum-likelihood (PRML) codeword. Decoding systems and methods are also provided.

Abstract: A hard disk drive with an encoder that writes data onto a disk in accordance with a plurality of first codes. Each code contains a plurality of digital bits. The first codes are selected so that if a bit is added or dropped during a write or read process the resulting bitstream can only be one of the selected first codes. This allows the bitstream to be accurately decoded to detect and correct for the added/dropped bit.

Abstract: A recording system, such as a magnetic or optical recording system, employs optimization metrics that are independent of a target partial response for equalization of a signal read from a recording channel. The optimization metrics employ samples adjacent to codeword boundaries of codewords representing encoded data, such as servo data, read from a recording medium. The optimization metrics are used to select filter parameters and/or tap weights for equalization. The filter parameters and/or tap weights might be derived based on the type of data read from the recording medium, the type of detector employed to detect the codewords of the read data, and the type of encoder/decoder employed for the read data.

Abstract: A method of how to perform logic operations on a hard disk drive with magnetic media capable of superimposing the binary information is invented. Such media contain magnetic particles with different anisotropy fields and different anisotropy axes orientations. Three magnetization states are utilized. The binary information is encoded as 0?> 00 and 1?> 11. In the beginning, strong magnetic fields created by the writing head record the first binary number on a track as the sequence of transitions between different magnetization states. All previous information is erased. Then, moderate magnetic fields are applied to the same track and reverse a part of magnetic particles writing the second binary number. As the result, we obtain superimposed transitions between different magnetization states. The reading sensor detects the magnetization transitions and gives the result of logic operations.

Abstract: A media includes a plurality of tracks, a preamble portion including a set of signals, a first servo burst having a first plurality of signals written substantially in phase with the preamble portion, and a second servo burst written out of phase with the preamble and the first servo portion. The media may be housed within a disk drive that includes a transuding head to read information from the media, and a read channel to read information from the disk including the information associated with the first servo burst and the second servo burst.

Abstract: A data recording/recovery device (20) comprises a packet generator (34) for including recordable information into a packet (44), the packet initially having a nominal run length limited (RLL) sequence if it were RLL encoded. A randomizer (38) uses a randomizer input value (50) to obtain a modified packet (46) which, when encoded, will at least partially have a different run length limited sequence than the nominal run length limited sequence. A write channel (40) records the modified packet (46) as a track packet at a destination physical location (42) on a storage medium (22). The randomizer input value (50) used to obtain the modified packet (46) is related to a predetermined physical location on the storage medium. In one example embodiment the randomizer input value is related to the destination physical location on the storage medium.

Abstract: A synchronous read channel having a single chip integrated circuit digital portion which provides digital gain control, timing recovery, equalization, digital peak detection, sequence detection, RLL(l,7) encoding and decoding, error-tolerant synchronization and channel quality measurement is disclosed. The integrated circuit accommodates both center sampling and side sampling, and has a high degree of programmability of various pulse shaping and recovery parameters and the ability to provide decoded data using sequence detection or digital peak detection. These characteristics, error-tolerant sync mark detection, and the ability to recover data when the sync mark is obliterated allow a wide variety of retry and recovery strategies to maximize the possibility of data recovery.

Abstract: A hard disk drive with an encoder that writes data onto a disk in accordance with a plurality of first codes. Each code contains a plurality of digital bits. The first codes are selected so that if a bit is added or dropped during a write or read process the resulting bitstream can only be one of the selected first codes. This allows the bitstream to be accurately decoded to detect and correct for the added/dropped bit.

Abstract: A read channel includes a signal receiver that receives a read back signal and a signal detector to detect symbols in the read back signal. The signal detector includes a first detector that generates raw decisions as a function of the read back signal, a post processor that identifies possible defects in the raw decisions, a selector that independently receives the raw decisions and a list of the possible defects from the first detector and the post processor, respectively, and a decoder that generates final decisions based on the raw decisions and the possible defects identified by the post processor. The decoder performs at least one of Reed-Solomon decoding, Bose Chaudhuri Hocquerghen (BCH) decoding and Hamming Decoding.

Abstract: A magnetic tape includes plural diagonal tracks, each storing a preamble sequence close to user data such that a transducer for reading the track reads the preamble sequence immediately before reading the user data. The preamble sequence is such that when the track is read by the transducer the preamble sequence has a power sequence with a power spectrum substantially equivalent to the power spectrum of the user data. An AGC circuit responds to the transducer.

Abstract: A method and apparatus reduces a DC level of an input word. The input word is divided into a plurality of components that include n symbols. The n symbols of the components are summed for each component. The component is encoded into a substitute component if a sum for the component exceeds a threshold. The components having a sum that does exceed the threshold are combined with at least one substitute component into an output word. An output word template is selected based on a number of substitute components and on a position that the substitute components originally occupied in the input word. The substitute components are inserted in the output word template. The components that have a sum that does not exceed the threshold are inserted in the output word template. Address and indicator symbols are inserted in the output word.

Abstract: A data read/write device includes a data write-processing unit that performs amplitude modulation on write data to obtain an amplitude-modulated signal that contains a plurality of amplitude levels, correlates a plurality of data included in the write data with each amplitude level of the amplitude-modulated signal to obtain amplitude data, and transmits the amplitude data to a magnetic head that writes the amplitude data into a memory area of a recording medium, and a data read-processing unit that reads the amplitude data via the magnetic head from each memory area of the recording medium, and converts the amplitude data into readable read data.

Abstract: In a coding method which does not restrict a run length of “1” while data is recorded/reproduced, there are such a drawback that when an error correction is carried out, a total number of error data to be corrected is increased, and also errors of not-detectable data are increased. While data is coded, a continuous number of “1” contained in a code word is limited, and then an error correction is carried out inside a coding/decoding process operation. Thus, a recording/reproducing apparatus having a small number of decoding errors is available.

Abstract: Circuitry for detecting excessive runs of similar bits of data in a data stream is provided. The data stream is typically received as serial data operating in a serial clock domain. Run-length detection circuitry checks the received data for run-length violations while operating in a slower parallel clock domain, as opposed to the faster serial clock domain. An advantage of operating run-length detection circuitry in the parallel domain is that longer length run-length violations can be searched for in the received data, as compared to run-length detectors that operate in the serial domain. Another advantage offered by the circuitry is that the run-length violation signal can be provided to utilization circuitry asynchronously. This enables utilization circuitry to quickly capture the signal despite differences in clock domains (i.e., the clock domain of the detection circuitry and the clock domain of the utilization circuitry).

Abstract: Non-uniform modulation encoding techniques are provided to prevent data from containing bit patterns that are prone to errors during read back. Modulation encoding is performed on a data stream to remove error prone bit patterns. Unconstrained data, such as error check parity, that is inserted into the modulated data stream may contain error prone bit patterns. Stricter modulation constraints are enforced on bits that are next to the unconstrained data, than on the remaining bits. By enforcing stricter modulation constraints on these bits, an entire data bit stream can have a desired modulation constraint.

Abstract: Techniques are provided for applying modulation constraints to data streams using a short block encoder. A short block encoder encodes a subset of the bits in a data stream. Then, the even and odd interleaves in a data stream are separated into two data paths. A first modulation encoder encodes the even interleave according to a first modulation constraint. A second modulation encoder encodes the odd interleave according to a second modulation constraint, which in general coincides with the modulation constraint for even interleave.

Abstract: A disk drive has timing marks (TMs) on the disk, that are chosen to reduce the probability of misidentification of a TM in the presence of read errors. The disk drive searches for TMs within a fixed TM search window which extends past the TM on the disk. A TM preferably maximizes the post-shift sliding distance for m post-shifts of the TM pattern, where m corresponds to the TM search window boundary. In this manner, the probability of a misidentification of the TM due to a post-shift having a small distance from the TM pattern is reduced. The TM pattern also provides pre-shift error resistance.

Abstract: The present invention is a disc drive storage unit incorporating novel apparatus, data structure and method for uniquely identifying data written during each write command operation of the disc drive storage unit. The disc drive storage unit attaches unique write identification data (sequence data, time data, or both) to host computer data written during each sector write operation. The unique write identification data is attached through independent action of the disc drive storage unit. The unique write identification data is attached to the host computer data in such a way that the unique write identification data is transparent to the host computer. The data structure relates the host computer data to the unique write identification data. The method documents the manner in which unique identification data is attached to, and detached from, the host computer data.

Abstract: Magnetic transfer can be performed with high reliability by shortening the magnetic transit interval of servo address information, that is, a section in which “0” or “1” continues. An area for registering information indicating a start position of data inversion or non-inversion of the servo address information is formed between a servo detection pattern and servo address information of the servo signal. When a continuing data section exceeds a predetermined section in a data sequence of the servo address information, the data at the subsequent portion to the exceeding position are inverted or non-inverted, and the exceeding position is registered as a start position for inversion or non-inversion in the area.

Abstract: Systems are provided for limiting channel control values, such as servo automatic gain control (AGC) values and/or servo phase lock loop (PLL) values, within respective desired ranges. Keeping such values within desired ranges improves servo demodulation robustness.

Abstract: Methods are provided for limiting channel control values, such as servo automatic gain control (AGC) values and/or servo phase lock loop (PLL) values, within respective desired ranges. Keeping such values within desired ranges improves servo demodulation robustness.

Abstract: A signal detector to detect symbols in a read back signal. The signal detector includes a first detector to generate raw decisions as a function of the read back signal. A post processor identifies possible defects in the raw decisions. A selector selects a portion of the possible defects and generates modified decisions based upon correcting the portion of the possible defects. At least one signal decoder generates final decisions as a function of the modified and raw decisions. A decision block returns control to the selector in response to detecting excess errors in the final decisions.

Abstract: Method and apparatus for detecting defects in a magnetic medium of a data handling system. The magnetic medium includes a number of user data wedges each disposed between an adjacent pair of servo data wedges. A predetermined data sequence is written to the user data wedges, and subsequently read to generate a readback signal. A sequence of discrete time sample values are generated from the readback signal. Defects in the medium are detected in relation to the magnitudes of the discrete time samples. A media scan controller outputs a first multi-bit information record having at least one bit composing the address of the user data wedge containing a defect, and a second multi-bit information record having at least one bit composing an address of the defect within the user data wedge. No information is written to the buffer when no defects are identified.

Abstract: Method and apparatus for recording data on a magnetic recording medium and writing data to a computer bus in which the data is divided into words of a predetermined length, a signal is generated for each data word, having an amplitude which is representative of the value of the data word, and this signal is then recorded to the magnetic recording medium or written to the computer bus. Complementary method and apparatus is provided for reading the data from the magnetic recording medium and the computer bus.

Abstract: A method of encoding and decoding data involving the simultaneous application of pulse width modulation and pulse position modulation systems to data intended for storage on a magnetic disk medium.

Abstract: A disk drive of perpendicular magnetic recording method including a read head comprising a GMR element and a drive using a double-layered disk medium, is disclosed. In the magnetic field response characteristic of the GMR element, the relationship between the degree of nonlinearity and a pulse width at 50% threshold (PW50) of a differentiated read signal is used. The degree of nonlinearity of the GMR element is adjusted such that the PW50 is smaller than the maximum value. The read channel comprises a differentiation circuit for converting the read signal output from the GMR element into the differentiated read signal.

Abstract: Circuitry for detecting excessive runs of similar bits of data in a data stream is provided. The data stream is typically received as serial data operating in a serial clock domain. Run-length detection circuitry checks the received data for run-length violations while operating in a slower parallel clock domain, as opposed to the faster serial clock domain. An advantage of operating run-length detection circuitry in the parallel domain is that longer length run-length violations can be searched for in the received data, as compared to run-length detectors that operate in the serial domain. Another advantage offered by the circuitry is that the run-length violation signal can be provided to utilization circuitry asynchronously. This enables utilization circuitry to quickly capture the signal despite differences in clock domains (i.e., the clock domain of the detection circuitry and the clock domain of the utilization circuitry).

Abstract: The present invention relates to method and apparatus of converting a series of data words into modulated signals. This method divides a data word, which a sync signal is to be added in front or rear of when it is written in a recording medium, into two or more word segments, generates for each word segment a number of intermediate sequences by combining mutually different digital words with that word segment, scrambles these intermediate sequences to form alternative sequences, translates each alternative sequence into a (d, k) constrained sequence, checks how many undesired sub-sequences are contained in each (d, k) constrained sequence, and selects one (d, k) constrained sequence for recording on an optical or magneto-optical recording medium among the (d, k) constrained sequences not having the undesired sub-sequence. Applying this method to a modulating device, DSV control can be conducted by much simpler hardware.

Abstract: A method of encoding and decoding data involving the simultaneous application of pulse amplitude modulation, pulse width modulation, and pulse position modulation systems to data intended for storage on a magnetic disk medium.

Abstract: A digital VFO phase control device comprising: an output signal generation means for generating an output signal having the predetermined phase relationship with an input signal of the digital VFO phase control device, a phase difference detection means for detecting a phase difference between the input signal and the output signal, a first correction value output means for outputting a correction value for correcting a phase of the output signal based on a phase difference detected by the phase difference detection means, a second correction value output means for outputting a preset correction value for correcting a phase of the output signal based on a phase difference detected by the phase difference detection means, a comparison means for detecting whether or not the phase difference detected by the phase difference detection means being within a predetermined range, and a correct value selection means for selecting either one of a correction value outputted by the first correction value output means and

Abstract: A method for write-precompensating a waveform for magnetically recording a waveform on a magnetic medium is disclosed. A user data stream is encoded into an encoded data stream so that the encoded data stream has no tribits and no consecutive dibits. No delay is applied to a first transition of a dibit of the encoded data stream. An isolated transition of the encoded data stream is delayed by a first predetermined amount of time. The second transition of a dibit of the encoded data stream is delayed by a second predetermined amount of time, such that the second predetermined amount of time is substantially twice the first predetermined amount of time. Preferably, the encoded data stream satisfies a predetermined run length limited (RLL) k− constraint of k=13 and a predetermined twins t-constraint of t=15. In one embodiment, the encoded data stream is encoded by a block code at rate 8:10. In another embodiment, the encoded data stream is encoded by a block code at rate 16:19.

Abstract: A magnetic recording and/or reproducing apparatus performing efficient decoding to lower a decoding error rate. A magnetic recording and/or reproducing apparatus 50 includes a modulation SISO decoder 63 for modulation decoding data modulation-encoded in a predetermined fashion by a modulation coder 52. In the magnetic recording and/or reproducing apparatus 50, the modulation SISO decoder 63 is a soft input soft output (SISO) type modulation decoder fed with a soft input signal and issuing a soft output signal. The modulation SISO decoder 63 is fed with a trellis soft output signal D64 supplied from a trellis SISO decoder 62 to find a soft decision value for an error correction coding data D52 fed to the modulation coder 52 of the recording system to generate a modulated soft decision signal D65. The modulation SISO decoder 63 routes the so-generated modulated soft decision signal D65 to a downstream side error correction soft decoder 64.

Abstract: The capacity and realized data rate of a data storage medium is increased by storing multiple bits per symbol using digital modulation techniques. Both phase and amplitude modulation techniques can be applied so that each symbol includes two or more bits that are represented by in-phase and quadrature phase portions of the signal corresponding to the data on the medium.

Abstract: The present invention relates to method and apparatus of converting a series of data words into modulated signals. This method generates for each data word a number of intermediate sequences by combining mutually different digital words with that data word, scrambles these intermediate sequences, translates each scrambled sequence into a (d,k) constrained sequence, detects running digital sum (RDS) every bit for each translated (d,k) constrained sequence while counting sign changes of each RDS, selects one sequence of which RDS changes most in sign among the (d,k) constrained sequences after discarding every sequence of which maximum value of RDS is beyond a preset threshold, and records the selected sequence onto a recordable medium such as an optical disk or a magneto-optical disk. The present invention can suppress DC component more remarkably in case that a sequence becomes longer.

Abstract: In a coding method which does not restrict a run length of “1” while data is recorded/reproduced, there are such a drawback that when an error correction is carried out, a total number of error data to be corrected is increased, and also errors of not-detectable data are increased. While data is coded, a continuous number of “1” contained in a code word is limited, and then an error correction is carried out inside a coding/decoding process operation. Thus, a recording/reproducing apparatus having a small number of decoding errors is available.

Abstract: A method of encoding a digital data stream for writing to a digital storage (DDS) format tape data storage medium comprises writing a byte stream to a preamble region, immediately preceding a user data region. The byte stream has a power spectrum substantially similar to a power spectrum of the user data region. An automatic gain control circuit responds to the preamble data stream in a substantially similar fashion to its response to the user data stream.

Abstract: Methods and apparatus for increasing the density of data storage on a magnetic medium by using variations in positioning of magnetic transitions to encode bits. Conventionally encoded bits are written to the medium as sequences of magnetic transitions according to an encoding standard. Additional bits are encoded on the medium as deviations from a nominal position of magnetic transitions separating conventionally encoded bits. The deviation from the nominal position is within an allowable range of tolerance for the standard followed in encoding the conventionally encoded bits. In order to prevent accumulation of error, additional bits are only encoded in transitions separating a pair of conventionally encoded bits. The first and last transitions of the pair do not have additional bits encoded as deviations of transition locations. This technique allows the encoding of one additional bit for every two conventionally encoded bits.

Abstract: A Viterbi detector receives a signal that represents a binary sequence having groups of no more and no fewer than a predetermined number of consecutive bits each having a first logic level, where the groups are separated from each other by respective bits having a second logic level. The Viterbi detector recovers the binary sequence from the signal by calculating a respective path metric for each of no more than four possible states of the binary sequence, and determining a surviving path from the calculated path metrics, where the binary sequence lies along the surviving path. Or, the Viterbi detector recovers the binary sequence from the signal by calculating respective path metrics for possible states of the binary sequence, calculating multiple path metrics for no more than one of the possible states, and determining the surviving path from the calculated path metrics.

Abstract: The present invention provides for the compression of digital and analog data for storage and transmission. Analog data in the form of an analog signal is converted into a digital signal by an analog-to-digital converter. The digital signal is then converted into an analog signal having an alternating frequency by a first converter processor and an alternating frequency generator according to a predetermined conversion table. To reproduce the original analog signal, the analog signal having an alternating frequency is first converted back into a digital signal by an alternating frequency measurement means connected to a second converter processor, also in accordance with the predetermined conversion table. The digital signal is then converted to the original analog signal by a digital-to-analog converter.

Abstract: The present invention comprises a magnetic recording system including a partial response, maximum likelihood recording channel incorporating fixed frequency read signal sampling and a digital timing control loop. Such a system is especially suitable in magnetic tape recording systems having a high degree of media speed variation during the read and write processes.

Abstract: The invention relates to a marking device (1, 11) for the identification of objects with a coding of regions (4, 5, 13) with different magnetic properties. The marking device is characterized in that magnetic regions (4, 5, 13) are so magnetically biased that their hysteresis loops (7, 8, 15) are shifted on the field strength axis (H) relative to the magnetization axis (M).

Abstract: Encoding tables are accorded with variable-length encoding rules using a variable constraint length. A DSV control bit is periodically inserted into a first input bit stream to generate a second input bit stream. Every m-bit piece of the second input bit stream is encoded into an n-bit output signal forming at least a portion of an output code word by referring to the encoding tables. Thereby, the second input bit stream is converted into a first output bit stream composed of output code words and observing RLL (d, k). A sync word is inserted into the first output bit stream for every frame to generate a second output bit stream. A frame-end output code word is terminated at a position before a next-frame sync word. DSV control of the second output bit stream is implemented in response to the inserted DSV control bits.

Abstract: An apparatus and method for transferring data between a read/write transducer and a data storage medium provides for improved track format efficiency. Data is written to a data sector of the data storage medium using a write current waveform developed in the read/write transducer. The write current waveform is typically at one of several possible states following writing of the data to the data sector. According to the present invention, a transition pattern is generated and used for transitioning the write current waveform from the state following writing of the data to a known state consistent with coding constraints of the data channel. A predetermined data pattern associated with the known state of the write current waveform is written to a pad field of the data sector. The transition pattern and the predetermined data pattern are used to resolve detector and parity post-processor closure decisions during a sector read operation.

Abstract: Reduction of the complexity of a Viterbi-type sequence detector is disclosed. It was based on elimination of less probably taken branches in the trellis. The method is applied to the design of the E2PR4 channel with 8/9 rate sliding block trellis code. Coding, by itself eliminates two states by coding constraints, and the disclosed method reduces the number of required ACS units from 14 to 11, while reducing their complexity as well. For the implementation of E2PR4 detection, 4 4-way, 3 3-way, 3 2-way and one 1-way ACSs are needed. System simulations show no BER performance drop at common SNRs when compared with a full 16-state E2PR4 implementation in magnetic disk drives.

Abstract: A disk drive system comprises control circuitry and a disk device. The disk device transfers a read signal representing user data, servo data, and auxiliary data to the control circuitry. The control circuitry detects encoded signals representing “0” and “1” auxiliary data bits from the read signal. The control circuitry decodes the encoded signals into the auxiliary data bits. The encoded signals representing the “0” auxiliary data bits have opposite polarity from the encoded signals representing the “1” auxiliary data bits. Polarity reversal pulses are between consecutive encoded signals with opposite polarities. The auxiliary data bits could be repeatable run-out data that is processed to generate a position signal that the disk device uses to compensate for repeatable run-out error.

Abstract: The invention is a modulation system that encodes symbols in accordance with a modulation code which, for a given communications channel, produces a signal that at the decoder includes maximized sample timing information in each encoded symbol. For systems that use PLLs to control a sample timing clock, the sample timing information is the average or squared slope. The modulation code used for a given system is selected based on the target response h(x) of the associated communications channel, such that h (x)*rk exceeds a predetermined threshold value, where “*” represents convolution and rk is a modulation code symbol. To reduce the bit overhead, or code rate, the inventive modulation system provides more modulation code symbols at the start of a data block, or sector, when system jitter is expected to be relatively high in response, for example, to the movement of a read head.

Abstract: A data storage apparatus for magnetic recording and regeneration on a medium. Only in case of a dibit or Tri-bit code sequence in MTR codes having a restricted number of magnetic transition consecutive, a write unit records the interval of the magnetic transition on the medium with an extension of &Dgr;T relative to the original magnetic transition interval. For the maximum likelihood detection after equalization of the medium read signals, a read unit adds to an expected value of the maximum likelihood detection an amplitude error &Dgr;V arising from the extension record of the magnetic transition interval relative to the original magnetic transition interval. A parameter regulation unit regulates and sets &Dgr;T and &Dgr;V by use of test patterns.