Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1997-08-27
2001-02-20
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S048000
Reexamination Certificate
active
06191902
ABSTRACT:
TITLE OF THE INVENTION
Magnetic disk apparatus and magnetic disk medium
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk apparatus for reading medium information by an MR head and, more particularly, to a magnetic disk apparatus which can properly recover a sync byte pattern at the head of a sector when such a sync byte pattern is lost by a thermal asperity ie. therefor collision heat generation (friction heat) occurring when the MR head comes into contact with a medium.
In recent years, in association with an increase in capacity of a magnetic disk apparatus as an external storage device of a computer, a magnetic head of a high performance is requested. As a magnetic head satisfying the request, attention is paid to a magnetic disk apparatus having what is called an MR head using a magneto-resistive element which can obtain a high reproduction output without depending on a peripheral velocity of a recording medium. In the magnetic disk apparatus using such an MR head as a read head, however, when the MR head collides with a physical convex or concave portion due to an extremely slight dent, a deformation, or the like on the surface of the medium which is rotating, a temperature of the MR head rises instantaneously by a friction heat. When the temperature of the MR head rapidly rises by the contact with the medium as mentioned above, a base line of a read signal is shifted, and a read error which cannot be recovered occurs. This state is seemingly the same as when a medium defect exists. The phenomenon in which the read error occurs by the collision heat generation of the MR head with the medium is usually called a thermal asperity. That is, when a state in which a sync byte pattern cannot be read as a result of thermal asperity of the MR head in a sync byte region in a read sector on a medium track, sector data cannot be demodulated at all. In this case, although the reading operation is executed again, since the defect caused by the thermal asperity of the MR head is a kind of physical defects, the same reading impossible state repetitively occurs in the same sync byte region and an unrecoverable read error is caused. For a high density recording of the medium, it is necessary to reduce a floating height of the MR head and this results in a factor of an increase in number of times of occurrence of the defect due to the thermal asperity of the MR head. As a rotational speed of the medium increases, when the thermal asperity of the MR head occurs, the shift of the base line of the read signal further increases. Further, every possible tests have been performed to the magnetic disk apparatus at a factory stage. The defect caused by the thermal asperity of the MR head is, however, a problem occurring during the use by the user. Further, since there is a tendency such that the defect grows while the user is using the apparatus, there is a fear that the performance of the magnetic disk apparatus remarkably deteriorates.
SUMMARY OF THE INVENTION
According to the invention, there are provided a magnetic disk apparatus and a magnetic disk medium which can realize a strong recovery for a defect caused by a thermal asperity of an MR head in a sync byte region.
It is an object of the invention to provide a magnetic disk apparatus for writing and reading information to/from tracks of a medium on a sector unit basis by using a combination head having a write head, for example, an inductive head and a read head, for instance, an MR head.
(Basic sector format)
A writing unit (write channel) of a magnetic disk apparatus of the invention splits a sync byte pattern into two patterns of a first sync byte pattern and a second sync byte pattern at the time of writing to a sector region, splits write data into two data of first data and second data, writes the first data subsequently to the first sync byte pattern, writes the second data subsequently to the second sync byte pattern, and finally writes an error detection correction code. When the first sync byte pattern is detected from read data, a reading unit (read channel) demodulates the subsequent first data, second data, and error detection correction code. When the first sync byte pattern is not detected but the second sync byte pattern is detected, the reading unit demodulates the subsequent second data and error detection correction code and reconstructs the lost first data by the error detection correction code. A data length of the first data arranged subsequently to the first sync byte pattern is equal to or longer than a length of defect caused by the thermal asperity of the MR head with the medium and is equal to or shorter than a length of data which can be corrected by the error detection correction code. Even if the loss of data occurs due to the thermal asperity of the MR head, therefore, either one of the split first and second sync byte patterns is lost and sector data can be read out by a normal detection of either one of them. That is, when the first sync byte pattern is lost, the second data and the error detection correction code are normally demodulated by detecting the subsequent second sync byte pattern and the lost first data can be recovered by the error detection correction code without a problem. When the second sync byte pattern is lost, the split data can be read out by detecting the first sync byte pattern without a problem. The first and second sync byte patterns are made different, thereby enabling each pattern to be certainly detected. The writing unit also writes a training pattern for automatically adjusting a circuit constant (tap coefficient) of an automatic equalizer (transversal filter) provided for the reading unit to an optimum value to a position before each of the first and second sync byte patterns. The writing unit also writes a pilot pattern for synchronizing a clock generating circuit provided for the reading unit with the read data to a position before each of the first and second sync byte patterns. Further, the writing unit has a scrambling circuit for scrambling each of the first and second data and, further, the error detection correction code to be written to the medium by using a predetermined pseudo random code (for example, M series code). In correspondence to the scrambling circuit, the reading unit has a descrambling circuit for descrambling the first and second data and the error detection correction code read out from the medium by using the pseudo random code. A gap pattern at a sector boundary can be also scrambled and descrambled.
When the first sync byte pattern is detected, after the first data is demodulated, the reading unit skips the demodulation of the second sync byte pattern and demodulates the second data and the error detection correction code. Specifically speaking, the reading unit presets the data length of the first data and the gap length from the first data to the second data, demodulates the first data for an interval of the data length after the end of the detection of the first sync byte pattern, and after that, skips the pattern detection for an interval of the gap length, and starts the demodulation of the second data. When the first sync byte pattern can be detected separately from the data demodulation, whether data has correctly been written at the position of the second sync byte or not is discriminated from the data length and the gap length. If the data is not correctly written, it is determined that the second sync byte pattern is not correct, and a read sector is regarded as a defective sector and is dealt as a target of an alternating process after completion of the reading process. When both of the first and second sync byte patterns cannot be detected, the reading unit executes the reading process again (retry). In the rereading process, a read gate is turned on at a position of a pilot pattern subsequent to the first data and the pattern detection is started. When the second sync byte pattern is detected, the subsequent second data and error detection correction code are demodulated and the first data is reconstructed by
Hashimoto Shuichi
Hashimura Yoshihiro
Fujitsu Limited
Greer Burns & Crain Ltd.
Kim W. Chris
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