How did Sony increase capacity on the existing Minidisc to 305MB?
Sony diagram from Hi-MD announcement Photo courtesy AV Watch Several changes were responsible for the increase in capacity: • The way data bits are encoded into bits on the disk (the modulation system) was changed from EFM (“Eight to Fourteen Modulation”, the Compact Disc’s method) to the more efficient RLL1,7 (typical of hard drives). • The readout electronics were changed from a simple peak detector to a more sophisticated Partial Response Maximum Likelihood (“PRML”) system that essentially uses digital signal processing techniques to extract the disk data signal from inter-symbol noise, allowing bits to be packed closer together. • The error correction system and “sector structure” were changed to increase data packing efficiency to 80% (Sony doesn’t mention what these changes were however). Changes #1 and #2 brought a factor of 1.38x, #3 brought 1.48x, for a total of 2.04x.
