Patent ID: 7646693

Claim:
A method for overwriting data in a probe-based data storage device wherein data is represented by the presence and absence of pits formed in a storage surface by a probe of the device, the method comprising: coding input data such that successive bits of a value x in the coded input data (b 0 , b 1 , b 2 , . . . ,) are separated by at least d bits of value {tilde over (x)}, where d is a predetermined number≧2; generating overwrite data bits (v 0 , v 1 , v 2 , . . . ,) by encoding the coded input data bits (b 0 , b 1 , b 2 , . . . ,) such that, if a pit represents a bit of value p in the data storage device, then: (a) any bit of value x in the coded input data (b 0 , b 1 , b 2 , . . . ,) is encoded as an overwrite data bit of value p; (b) any bounded run of L≦2d bits of value {tilde over (x)} in the coded input data (b 0 , b 1 , b 2 , . . . ,) is encoded as a run of L overwrite data bits of value {tilde over (p)}; and (c) any bounded run of L>2d bits of value {tilde over (x)} in the coded input data (b 0 , b 1 , b 2 , . . . ,) is encoded as a run of L overwrite data bits consisting of n bits of value p and (L−n) bits of value {tilde over (p)} where n=CEIL[(L−2d)/d] and the n bits are positioned in the run such that: (c1) there is a bit of value p within d bits of the end of the run; (c2) there is a bit of value p within 2d+1 bits of the beginning of the run; and (c3) for n>1, each of the n bits is within d bits of another of the n bits; and overwriting data on the storage surface with the overwrite data bits (v 0 , v 1 , v 2 , . . . ,) at a bit spacing such that writing an overwrite data bit of value p can erase an existing bit of value p within d bits of that overwrite data bit.