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A subdivision of a track on a magnetic disk that represents the smallest portion of data that can be modified by overwriting. Each sector has a unique address, which contains the location of the track and the sector number. In order to read an address or data the drive decoding electronics must be synchronized to the data stream. To achieve this a special pattern, the preamble, is written. Following the preamble comes the address mark or data mark as appropriate.

A disk may be soft-sectored or hard-sectored. In soft-sectoring, the size and position of the sectors is determined by the control electronics and software: disk drives generate an index signal once per revolution of the disk, and when this is received from the drive unit all the sectors of a track are written in one continuous operation. On a hard-sectored disk, the start of each sector is related to a sector signal generated by the disk drive and is positively related to the position of the disk. Hard-sectoring can achieve higher packing of sectors since it is not necessary to have large intersector gaps to accommodate speed variations.

Subjects: Computing.

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