RUN-OUT ZONE DECIDING METHOD FOR MAGNETIC DISK

PURPOSE:To decide a run-out zone without fail by moving a magnetic head for 1/2 of a track interval and detecting the erase gap of other constant number or above in succession to the number of times set beforehand. CONSTITUTION:An erase gap detecting circuit 11 counts the number of times in which the reading signal of the period is not outputted each time a magnetic disk 1b is rotated once, and outputs it as a counted value. A microcomputer 13 reads the counted value and discriminates whether or not the counted value is 16 or above. Here, for example, a head position when 16 erase gaps are detected is H3, and then, 16 erase gaps are detected in the same way even at the position of H4 in where an 1/2 track is moved. Thus, when a head position enters the run-out zone and 16 erase gaps are once detected, they are in the same way detected without fail even after the 1/2 track is moved and at this time, it is decided that the position arrives at the run-out zone.