International Business Machines Corporation

Takao Matsui

Hiroaki Suzuki

Kenji Kuroki

Hideo Asano

Kenji Ogasawara

Tatsuya Endo

Koji Kurachi

Yoshiaki Sonobe

Kenji Okada

Takashi Nakamura

Akira Kibashi

Makoto Takase

Yuji Yokoe

Hiromi Nishimiya

Yoshiro Amano

Kazushi Tsuwako

Yuji Kigami

Tsutomu Numata

Kaoru Umemura

Katsumi Suda

Katsushi Yamaguchi

Masaomi Ikeda

Tatsuya Endoh

Tsuyoshi Miura

Mayumi Okada

Akira Shibata

Junji Hashimoto

An RW offset setting method which includes recording a test pattern by a write head, reading the test pattern by a read head, measuring an amplitude of a read back signal at each tracking position, finding an approximate expression of a profile of the measured amplitude, finding a tracking position, and finding a RW offset based on this tracking position, setting a RW offset for all tracks in the disk device based on the RW offsets about the plurality of tracks to be measured. A read data error recovery method that includes the steps of determining an off-track direction where the amplitude increases, searching an off-track position where the amplitude becomes a local maximum, measuring the amplitude at each off-track position reading data recorded in the data sector.

System and method for setting a read/write offset and for recovering from data read errors

A method and apparatus for recovering from operation errors arising in an information recording and reproducing unit using a head with a GMR sensor is described. The read and write operations of the unit comprise executing a first error recovery procedure for recovering the operation error, executing a first GMR evaluation procedure for evaluating the performance of the GMR sensor when the operation error cannot be recovered by the first error recovery procedure, and applying a resetting pulse to the GMR sensor in accordance with the first GMR evaluation procedure.

Error recovery in unit using GMR sensor

In accordance with the present invention, the initialization for orienting the magnetized directions of the free layers of GMR heads (mounted on the diagonally shaded surface of sliders,) by an external magnetic field is again executed also for the opposite direction, thereby to increase the yield of the GMR heads. Further, it is determined whether the magnetized direction of the pinned layer of GMR heads can be once reversed to the opposite direction, thereby to select damaged GMR heads at an early stage. Then, by performing a reset while performing a quasi-static test for seeing the read back response of the GMR head after restoring the magnetized direction of the pinned layer to a positive rotation, a safe and efficient reset is executed. The reset can be executed not only by applying only a pulse, but also while providing an external magnetic field in the pinning direction, or only by giving a high magnetic field. A tool,can be commonly used for the initialization, reset, or read back response through each process level. For the quasi-static test, coils,, and,are selectively used as Helmholz coils.

Methods for initializing and/or resetting GMR heads by applying oppositely directed magnetic fields

A preamplifier circuit to improve the ESD immunity of magnetic recording devices having magnetoresistive (MR) sensors, without degrading the sensor's high-frequency characteristics. The preamplifier circuit is coupled to an MR sensor having one terminal grounded. The preamplifier circuit includes a varistor coupled between a power supply line and a ground terminal. If a high voltage, exceeding the varistor voltage, is applied to the chassis (ground), it is discharged through the varistor between the power supply voltage line and the ground terminal, instead of through the MR head or the arm electronics module. The present invention thereby protects the MR head and the arm electronics module from ESD damage.

Preamplifier circuit with magnetoresistive sensor ESD protection

A magnetoresistive (MR) reproduction element is positioned during data recording, data reproduction, and formatting so that its total range of movement is 3/2 times a range of movement (microjogging) from the location of the reproduction element in data recording to the location of the reproduction element in data reproduction. The total range of movement is centered within a range where the detection of positional error of the reproduction element changes linearly. Therefore, in the respective data recording, data reproduction and formatting processes, microjogging is performed and the detection of positional error changes linearly for each of an off-track OF.sub.W in data recording, an off-track OF.sub.R in data reproduction, and an off-track OF.sub.F in formatting. Accordingly, the characteristics of the MR reproduction element can be effectively used to a maximum degree and information can be reproduced without being undetected or erroneously detected.

Magnetoresistive head and hard drive system having offsets from center

A controller 40 of an HDC 30 is connected to a drive 28, and an arm is rotated through a predetermined angle. A magnetic head 20 on the arm comprises a recording element and a reproduction element. A bias current is supplied to the magnetic head 20 from the controller 40 through a driver 36A and a switching circuit 32A, and the magnetic field of the disk 18A is detected in a detector 38A through a switching circuit 32A. The switching circuit 32A inverts the polarity of a current applied to the magnetic head 20A, by a signal from the controller 40 corresponding to a skew angle. Accordingly, the direction of the bias magnetic field is changed, the effective sensitivity position of the reproduction element approaches the recording element, and off-track can be reduced.

Magnetoresistive head bias current switching based on skew angle

A disk drive having embedded servo information accesses data without using sector identifier recorded in each sector. When a signal sector pulse signal (SP) at the end of a servo area is detected in a dead state during start up, a first data state for the start of a sector transits to a second data state for the litter region of the sector being divided in accordance with the capacity stored in a current sector's pointer register. At the beginning of the sector, the contents of a next sector's pointer register is stored in current sector's pointer register and the contents of a next sector's operation register is stored in a current sector's operation register. Upon completion of sector processing, the first data state is maintained when the next sector is contiguous. When a terminate instruction is stored in current sector's operation register, the process moves to dead state. When the servo area arrives, the process moves to idle state. Responsive to this state, the magnetic head is activated to enable read and write operation for sectors having no sector identifier on the disk.

Information recording disk and drive system using no sector ID to

Disclosed is a disk drive having at least one disk. An actuator arm carriers at least two sliders which are positioned over the first and second surface of the disk. The actuator arm moves the sliders to various selected positions over disks so that representations of data can be read from or written into the tracks of the disk. Each slider includes at least one magnetic transducer or magnetic head. The magnetic head is actually passed over the track in the disk during a read or write operation. The heads are shifted slightly with respect to a line perpendicular to the disk surface to minimize or reduce crosstalk and electromagnetic coupling between the heads located on the first and second surface of the disk. In other words, the heads are intentionally misaligned to increase the distance between the two heads and to reduce crosstalk and electromagnetic coupling between the two heads.

Magnetic disk apparatus having recording heads for opposite disk

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Yamato, Japan

Takao Matsui