Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Patent
1988-09-21
1990-06-12
Wolff, John H.
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
360 7705, 360 7808, G11B 2110
Patent
active
049337866
ABSTRACT:
A fault tolerant servo index scheme is described. The present invention provides a servo index pattern and detection method which can be utilized to any servo scheme, including, but not limited to, sector servo and dedicated surface servo. The servo pattern of the preferred embodiment of present invention is a twelve bit pattern chosen to limit the side lobes of an autocorrelation plot of the pattern with a template of the pattern. In this manner a greater number of errors can be tolerated while still permitting index identification. Initially, the entire servo pattern on a servo track is detected in sequence at the bit rate. Each twelve bit sequences of bits is compared to a template of the servo pattern and the number of bits whose position and value ("1" or "0") match the template are determined. Whenever a threshold level (less than the total number of bits in the pattern) of "hits" takes place it assumed that the index has been detected. By minimizing the magnitude of the side lobes of the correlation plot, the threshold can be set between somewhere between complete correlation and the side lobe number. The lower the side lobe, the greater the number of errors which can be tolerated while still indicating an index identification. In one embodiment of the present invention, twelve bit sequence of the servo pattern are compared to a sequential series of templates in which a three bit burst error is implemented. Therefore, even if three consecutive index pattern bits are damaged the index can still be detected.
REFERENCES:
patent: 4636885 (1987-01-01), Yamada et al.
patent: 4638384 (1987-01-01), Stewart et al.
patent: 4682253 (1987-07-01), Leslie
patent: 4797757 (1989-01-01), Haitani
patent: 4811135 (1989-03-01), Janz
Maxtor Corporation
Wolff John H.
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