Abstract: A set of servo patterns on two or more servo tracks, at least one of which is adjacent to a data track, is described. One or more servo patterns in the set are inverted copies of one or more upright servo patterns in a different servo track. Using this set of servo patterns to calculate a position error signal (PES) for a servo head reduces error in PES calculations due to variations in media velocity.

Abstract: A magnetic field strength detector includes a magnetic field sensing element that outputs voltage as a function of magnetic field strength. In some embodiments, the magnetic field sensing element comprises a coil, and voltage is induced across the coil as a function of the magnetic field strength. A magnetic field strength detector also includes an indicator that alters as a function of the voltage output by the magnetic field sensing element when the magnetic field strength exceeds a threshold. The alteration is substantially irreversible and, in some embodiments, visible. The detector may be used to, for example, measure the strength of a magnetic field generated by a degaussing device, or to confirm that a particular medium was exposed to a magnetic field with a strength adequate to degauss the medium.

Abstract: The invention is directed to a servo writing apparatus having accurate alignment of write gaps of servo write heads. In particular, the write gaps substantially align in a servo channel corresponding to a servo band of a magnetic data storage tape. The servo band is fully magnetized (a.k.a. DC erased) in one direction by a direct current (DC) magnetic field across the write gap of one of the servo write heads. Time-based servo markings magnetized in a second direction are recorded on the fully magnetized servo band by a pulsed magnetic field across the write gaps of the other servo write head. The servo write heads may be mounted in a mounting structure within the servo writing apparatus. Maintaining a large mounting structure width to servo write head separation distance ratio improves write gap alignment accuracy, which assures full servo signal strength across the servo band without magnetizing adjacent data bands.