Data overwriting in probe-based data storage devices

摘要

Methods are provided for overwriting data in a probe-based data storage device (1) wherein data is represented by the presence and absence of pits formed in a storage surface (4) by a probe of the device. Input data is first coded such that successive bits of a first value in the coded input data are separated by at least one bit of the other value. Overwrite data bits v0, v1, v2, . . . , are generated from the coded input data bits b0, b1, b2, . . . , and the overwrite data bits v0, v1, v2, . . . , are then used to overwrite data on the storage surface (4). According to a first method, the overwrite data bits are generated such that, if a pit represents a bit of said first value in the data storage device (1) then vi={overscore (bi-1, for i>=1 and v0 has said first value, and if a pit represents a bit of said other value in the data storage device (1) then vi=bi-1 for i>=1 and v0 has said other value. According to a second method, the overwrite data bits are generated such that, if a pit represents a bit of said first value in the data storage device (1) then vi={overscore (bi-1({overscore (bi-2+bi) for i>=2, v0 has said first value and v1={overscore (b0, and if a pit represents a bit of said other value in the data storage device (1) then vi={overscore ((b)}i-1({overscore (bi-2+bi)) for i>=2, v0 has said other value and v1=b0. With both methods, the result of the overwrite operation is to record either the coded input data b0, b1, b2, . . . , or its complement {overscore (b0, {overscore (b1, {overscore (b2, . . . , depending on whether a pit represents a bit having the first value or a bit having the other value. This result is independent of the bit values of the data which is overwritten.