Patent ID: 7675703

Claim:
A magnetic recording disk drive comprising: a rotatable magnetic recording disk having a plurality of generally circular data tracks, each data track patterned into discrete magnetizable data blocks, and a plurality of generally equally angularly spaced servo sectors extending generally radially across the data tracks and containing timing marks, the timing marks comprising servo timing marks (STMs) and automatic gain control (AGC) marks; a write head for generating write pulses to magnetize the discrete data blocks; a write clock coupled to the write head for controlling the write pulses to the discrete data blocks; a read head for sensing the timing marks; timing mark detection circuitry coupled to the read head for measuring a write clock timing error between successive timing marks during rotation of the disk and comprising a phase detector for measuring the phase difference between the signal from the AGC marks and a reference signal, said reference signal being derived from the write clock, said phase difference representing a fractional part of a write clock cycle; and timing error compensation circuitry responsive to the timing error for adjusting the write clock.