Abstract: In a partial-response maximum-likelihood (PRML) signal detection and processing technique, reduction of data detection error events caused due to medium noise is achieved. For a PRML detection data result obtained after PRML data demodulation, a code error event that depends on a signal distance, and which has a high frequency of occurrence, is noticed and its occurrence probability is estimated. A locally-existing medium noise quantity is estimated from preceding and subsequent code patterns of the PRML detection data result. Based on this, the occurrence probability of the error event is compensated to improve the detection precision. As a result, data modulation with reliability higher than conventional maximum likelihood detection can be realized with a simple circuit structure.

Abstract: Two levels of error correction decoding are performed using first and second level decoders. A composite code formed by combining an inner component code and an outer component code can be used to decode the data and correct any errors. Performing two level decoding using a composite code allows the size of the inner parity block to be reduced to a single Reed-Solomon symbol while keeping a good code rate. The first level decoder generates soft information. The soft information can indicate a most likely error event for each possible syndrome value of the inner component code. The soft information can also include error metric values for each of the most likely error events. The second level decoder generates corrected syndrome values based on the soft information using the outer component code. The most likely trellis path that corresponds to the corrected syndrome values is then selected.

Abstract: An error correction encoder inserts redundant parity information into a data stream to improve system reliability. The encoder can generate the redundant parity information using a composite code. Dummy bits are inserted into the data stream in locations reserved for parity information generated by subsequent encoding. The error correction code can have a uniform or a non-uniform span. The span corresponds to consecutive channel bits that are within a single block of a smaller parity code that is used to form a composite code. The span lengths can be variant across the whole codeword by inserting dummy bits in less than all of the spans.

Abstract: For the purpose of letting through a magnetic flux which reverses the magnetization of the magnetic layer of the magnetic disk, a write element requires a predetermined sectional area. However, if a cross section of a magnetic pole is structured as the one having a large aspect ratio, the pole becomes less capable of letting the magnetic flux through effectively. This phenomenon brings about a lower limit on the track width of the magnetic poles and the track density cannot be raised. In the present invention, by making the width of the write element larger than the track pitch and securing a write magnetic field strong enough to reverse the magnetization of the magnetic layer, and further by writing while shifting a write head comprising the write element, a magnetic disk drive, of which the track width is narrower than the write element width, and the storage capacity is large, is realized.

Abstract: A method of enhancing the thermal stability of gray codes is disclosed. The gray code block in a servo area is recorded with a combination of two different magnetization directions. When the two different magnetization directions are expressed as “+” and “?”, the information “1” is recorded as “++??” or “??++” with the information “0” recorded as “+?+?” or “?+?+”. Since the filter for gray code demodulation is provided with a perpendicular recording mode, the servo area does not use long-wavelength signals that are susceptible to thermal demagnetization. As a result, thermal stability is enhanced.

Abstract: In a method of servo writing of a magnetic recording system and the magnetic recording system, the signal is recorded in a dummy area with a higher recording density than the burst signal. Also, the maximum bit length of the burst area is shortened as compared with the maximum bit length of the data area. A servo control method for perpendicular recording similar to that for longitudinal recording can be used to reduce the development cost. The anti-signal decay performance is also improved. Further, since the variations of the burst signal along the track width is suppressed, the positioning accuracy is improved. These effects combine to produce a reliable magnetic recording system of large capacity.

Abstract: In a partial-response maximum-likelihood (PRML) signal detection and processing technique, reduction of data detection error events caused due to medium noise is achieved. For a PRML detection data result obtained after PRML data demodulation, a code error event that depends on a signal distance, and which has a high frequency of occurrence, is noticed and its occurrence probability is estimated. A locally-existing medium noise quantity is estimated from preceding and subsequent code patterns of the PRML detection data result. Based on this, the occurrence probability of the error event is compensated to improve the detection precision. As a result, data modulation with reliability higher than conventional maximum likelihood detection can be realized with a simple circuit structure.

Abstract: The present invention discloses an information processing method including the following steps: (1) a first step receiving an encoded information data series as input; (2) a second step selecting a candidate decoded data code series from a first candidate decoded data code series group, decoding the encoded information data series, and generating a first decoded data code series; (3) a third step detecting a position and contents of erroneous decoded data codes in the first decoded data code series that cannot exist in the information data code; (4) a fourth step correcting the erroneous decoded data code and generating a corrected data code; (5) a fifth step selecting a single decoded data code series out of a second candidate decoded data code series group, decoding the encoded information data code series again, and generating a second decoded data code series; (6) The second candidate decode data code series group includes candidate decoded data code series from the first candidate decoded data code se

Abstract: In a method of servo writing of a magnetic recording system and the magnetic recording system, the signal is recorded in a dummy area with a higher recording density than the burst signal. Also, the maximum bit length of the burst area is shortened as compared with the maximum bit length of the data area. A servo control method for perpendicular recording similar to that for longitudinal recording can be used to reduce the development cost. The anti-signal decay performance is also improved. Further, since the variations of the burst signal along the track width is suppressed, the positioning accuracy is improved. These effects combine to produce a reliable magnetic recording system of large capacity.

Abstract: A method of enhancing the thermal stability of gray codes is disclosed. The gray code block in a servo area is recorded with a combination of two different magnetization directions. When the two different magnetization directions are expressed as “+” and “?”, the information “1” is recorded as “++??” or “??++” with the information “0” recorded as “+?+?” or “?+?+”. Since the filter for gray code demodulation is provided with a perpendicular recording mode, the servo area does not use long-wavelength signals that are susceptible to thermal demagnetization. As a result, thermal stability is enhanced.

Abstract: A magnetic disk apparatus including: a disk holding data as magnetic information on a magnetic recording film; a head to perform writing and reading of the magnetic information; a rotary actuator to move the head in a radial direction of the disk; plural heat elements in the head to locally heat the disk; a write element in the head to apply a magnetic field to the disk; and means for selecting at least one heat element from the plural heat elements, wherein the means for selecting the heat element selects at least one heat element from the plural heat elements so as to bring a center line of an area heated by the heat element and a center line of the position of the magnetic field generated by the write element into approximate correspondence, in correspondence with a relative angle between the head and a direction of movement of the disk.

Abstract: In the present invention, by making the width of the write element larger than the track pitch and securing a write magnetic field strong enough to reverse the magnetization of the magnetic layer, and further by writing while shifting a write head comprising the write element, a magnetic disk drive, of which the track width is narrower than the write element width, and the storage capacity is large, is realized.

Abstract: In a data demodulating method, predetermined input data is demodulated based upon a response characteristic of the partial response class 4; the demodulated input data is discrete-filtered to thereby produce filtering data; and the filtering data is maximum likelihood-decoded to thereby produce asymmetrical response data. Further, a magnetic recording/reproducing apparatus is arranged by using this data demodulating method.

Abstract: In a thermal assisted type magnetic disk apparatus having a head holding a heat element and a write element, in which coercivity of a disk is locally reduced by temperature-increasing the disk and writing is performed by the write element, along with a seek operation to move the head by a rotary actuator in a radial direction, a yaw angle is changed and a heat area and the write element are track-shifted. A mechanism to offset one of the heat area and the write element in a width direction of a slider, to array the heat element and the write element in a track running direction in correspondence with the yaw angle of the head.

Abstract: In a partial-response maximum-likelihood (PRML) signal detection and processing technique, reduction of data detection error events caused due to medium noise is achieved. For a PRML detection data result obtained after PRML data demodulation, a code error event that depends on a signal distance, and which has a high frequency of occurrences, is noticed and its occurrence probability is estimated. A locally-existing medium noise quantity is estimated from preceding and subsequent code patterns of the PRML detection data result. Based on this, the occurrence probability of the error event is compensated to improve the detection precision. As a result, data modulation with reliability higher than conventional maximum likelihood detection can be realized with a simple circuit structure.

Abstract: A method of enhancing the thermal stability of gray codes is disclosed. The gray code block in a servo area is recorded with a combination of two different magnetization directions. When the two different magnetization directions are expressed as “+” and “?”, the information “1” is recorded as “+?+?” or “?+?+” with the information “0” recorded as “+?+?” or “?+?+”. Since the filter for gray code demodulation is provided with a perpendicular recording mode, the servo area does not use long-wavelength signals that are susceptible to thermal demagnetization. As a result, thermal stability is enhanced.

Abstract: A magnetic recording/reproducing apparatus includes a partial-response equalization circuit having frequency characteristic of cutting off low-frequency signal components inclusive of DC components; and a maximum-likelihood decoder, in which a reproduced signal outputted from the reproducing head is processed by the partial-response equalization circuit and then inputted into the maximum-likelihood decoder to be data-reproduced, thereby reducing a noise and distortion on the reproduced signal and reducing a data detection error rate.

Abstract: Embodiment of the invention is to make the number of interleave sequences and the number of redundant bits as small as possible without increasing the number of bits per symbol so much. By encoding data into an error-correcting code by using an algebraic geometric code consisting of an algebraic curve surface having a genus g over a projective plane Pc?1(GF(2m)), where m is a positive integer, the code up to a length of 2m+21+m/2 g is constructed. In particular, by using a “Fermat code,” a version of the algebraic geometric code, consisting of a Fermat curve “C(L): XL+YL+ZL=0” over the P2(GF(22m)), where (m, L)=(5, 11), 4-Kbyte data constituting one sector can be encoded into the code made up of 10-bit symbols.

Abstract: A magnetic recording/reproducing apparatus includes a partial-response equalization circuit having frequency characteristic of cutting off low-frequency signal components inclusive of DC components; and a maximum-likelihood decoder, in which a reproduced signal outputted from the reproducing head is processed by the partial-response equalization circuit and then inputted into the maximum-likelihood decoder to be data-reproduced, thereby reducing a noise and distortion on the reproduced signal and reducing a data detection error rate.

Abstract: A digital magnetic recording/reproducing apparatus includes an LVA (List Viterbi Algorithm) detector which produces first to nth best sequences (n>1) of a decoded result, and replaces a likelihood ratio and a path memory of the ith best sequence (i=2, 3, . . . , n) with those of the (2i?1)th best sequence when contents of path memories of the (i?1)th and ith best sequences are equal to each other and an absolute value of a difference between likelihood ratios of the (i?1)th and (2i?1)th best sequences is smaller than a decision threshold. Alternatively, the LVA detector initializes a likelihood ratio of the ith best sequence to be a likelihood ratio of the (i?1)th best sequence with a constant difference value added thereto when contents of path memories of the (i?1)th and ith best sequences are equal to each other.