A data storage device (40) comprises a cartridge receiving stop (53) having a substantially flat middle surface (57) and angled outer edges (55a, 55b) for inhibiting the insertion of incompatible disk cartridges into the data storage device. A disk cartridge (10) adapted for use in the data storage device has opposite front corners (20c, 20d). The opposite front corners of the disk cartridge have a non-square shape adapted to avoid interference with the angled outer edges (55a, 55b) of the cartridge receiving stop (53). The data storage device may further comprise means for enabling a function of the data storage device (40) upon insertion of a disk cartridge (10) having non-square front corners into the disk drive. The disk cartridge may further comprise a projection (20a) positioned on the front peripheral edge (20) of the disk cartridge (10, 11, 15) and adapted to engage an operating member (158, 164, 182) of the enabling means on the substantially flat middle surface (57) of the cartridge receiving stop (53).