Disk drive system and removable disk cartridge adapted for downward compatibility

A higher-capacity disk drive system (101) and a higher-capacity removable disk cartridge (106) adapted for downward compatibility with older, lower-capacity disk drive systems, wherein a unique control format (208) is stored on higher-capacity removable disk cartridges (106) to distinguish them from older, lower-capacity removable disk cartridges (104) and thereby to facilitate cartridge capacity recognition by the higher-capacity disk drive system (101). Upon recognizing the capacity of an inserted removable disk cartridge, the higher-capacity disk drive system (101) can read and write data to the removable disk cartridge such that data which it stores on a lower-capacity removable disk cartridge (104) may be read by lower-capacity disk drive systems.