| 摘要 |
PROBLEM TO BE SOLVED: To provide a logical data length shorter than a physical data length, then to set a remaining physical data area as an effective data area, and to enable to read data recorded in a data area even when reading from a servo area is impossible. SOLUTION: A plurality of index sector pulse signals ISP are formed by timings different from one another based on first servo information Sn, and first data IDn writing/reading control is performed based on the plurality of index sector pulse signals ISP. Also, when the reading of second servo information S(n+1) is impossible, index sector pulse signals ISP are formed for second data ID(n+1) based on the first servo information Sn, and the second data ID(n+1) is read.
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