Thermal asperity pointer for servo sector

Abstract

A direct access storage device (DASD) servo control system controls movement of a magneto-resistive (MR) read/write head in response to a readback signal generated when the MR head repeatedly passes adjacent multiple servo fields and data fields of the recording medium. The servo control system receives multiple data samples, detects a thermal asperity in the readback signal when the MR transducer is adjacent a servo field of the recording medium, determines that the servo field data samples affected by the thermal asperity are invalid due to possible data errors, and operates a servo demodulator in response to the servo field thermal asperity before the MR transducer is next adjacent the servo field. In a DASD with a rotating disk, for example, the thermal asperity response can be implemented before one revolution of the disk has been completed after the thermal asperity is encountered. This permits data samples that have been corrupted by the thermal asperity to be ignored from servo processing, thereby reducing the uncertainty in the servo information being processed. If desired, the response can be implemented before the next servo sector is encountered. In this way, the DASD more effectively utilizes storage system resources and, in particular, handles thermal asperities more efficiently.

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