Signal-to-noise limitations of particulate disc coatings

Within the next decade advanced digital disc memory sub-systems will exhibit capacities in the range of one to five billion bytes per spindle. The corresponding areal densities required for such capacities will be in the range of 1.55 to 7.75 × 10⁶flux changes/cm²(10 to 50 × 10⁶flux changes/inch²). The limitation in areal density is determined by the acceptable error rate. The error rate is proportional to the pattern induced peak shift and inversely proportional to the signal-to-noise ratio in practical systems. Therefore, the limitations of particulate coatings are primarily related to the head/media interface characteristics which determine the system peak shift and signal-to-noise. This paper provides a formalism which relates signal-to-noise, peak shift and error rate along with a signal-to-noise budget for current disc system configurations. Projections of future areal densities are made from measurements on improved media. Comparison with the Shannon limit is considered for current disc systems.