When a FORMAT COMMAND is executed, a track density data indicating a track density of 96 TPI or 48 TPI is written into a discrimination area of a disk. When the disk is set into the FDD and is used, a CPU reads out track density data from the disk and produces a flag byte data, including the track density...http://www.google.fr/patents/US4644418?utm_source=gb-gplus-shareBrevet US4644418 - Floppy disk control apparatus
