Importance

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Abstract

A method and apparatus for locating more accurately the beginning of data cells stored on a medium with embedded servo sectors and improving the efficiency with which data can be stored on a medium as a consequence of more accurately locating the beginning of data cells stored on the medium. A counter counts the number of cycles of a clock. Initially, the counter is reset to zero upon recognition of a valid servo identification pattern (SID). When a terminal count value representative of the elapse of time until the end of a servo sector is reached, the counter is loaded with a negative value and continues to count. Upon detecting the next SID, the value of the counter should be equal to zero if an estimated time between detection of the last SID and the current SID was equal to the actual time between detection of the two SIDs. If the value of the counter is positive, then the current SID arrived under the head later than expected. In response, the value that is to be loaded into the counter upon the counter reaching terminal count is decremented. If the value of the counter is negative, then the current SID was early. Accordingly, the value to be loaded into the counter after terminal count is reached is incremented. Incrementing or decrementing the value to be loaded into the counter corrects for errors in the rotational velocity of the medium.

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First Claim