A zone-bit-recording disk drive has a rotating platter with a surface which is divided into at least two zones each having a respective different number of angularly spaced sectors therein. A method and apparatus for positioning the head relative to the platter surface involve maintaining a count of...http://www.google.com.au/patents/US5257143?utm_source=gb-gplus-sharePatent US5257143 - Method and apparatus for positioning head of disk drive using zone-bit-recording
