Write Synchronization in Bit-Patterned Media

Writing bit-patterned media has been a challenging problem because it is necessary to synchronize write timing with physical bit-pattern locations on disk. This timing requirement must be addressed not only in disk drives but also in testing environments such as a spin stand. This paper first describes a technique for synchronizing write timing on a spin stand. Testing results show that, with data block length similar to a disk drive sector, the write timing jitter due to synchronization error is much smaller than the magnetic transition jitter. We then discuss the potential timing jitter sources in a disk drive, including disk speed variation, head vibration, and write clock stability. Experimental data show that the head vibration is potentially the most difficult jitter source for the write clock to handle. The possibility and difficulty in applying coding techniques to correct write timing error is also investigated. While it is possible to create codes for this purpose, practical considerations can limit its usefulness.