A removable record disk apparatus with rotational position control.

摘要

In a record disk apparatus which has a motor-driven spindle (31) for removably receiving a record disk (30) having an index mark as the sole circumferential position indicator, the spindle (31) is provided with a tachometer member (31T) with marks angularly displaced a distance equal to the disk storing a predetermined number of bytes on the record tracks. A byte counter (12) counts byte periods and is reset by each of the tachometer marks for indicating offset of the marks from the index signal. A register (17) stores the offset as determined by the count in the byte counter at index time. A segment counter (20) counts tachometer pulses for indicating which of the segments are currently being scanned on the record disk. The segment count when coupled with an offset indication provides true rotational position to a byte granularity. The index pulse resets the tachometer counter to zero. The segment counter (20) has a modulus equal to the number of groups of bytes (segments) in each of the record tracks.