Abstract: A magnetic disk cartridge includes a magnetic disk and a casing which accommodates therein the magnetic disk. The casing has a magnetic head opening through which a magnetic head gains access to the magnetic disk and a sliding shutter which slides between a closed position, where it covers the magnetic head opening, and an open position, in which the magnetic head opening is uncovered. The sliding shutter is provided with a first cutaway portion which is formed on the front edge of the shutter and can be engaged with a shutter opening pin which is provided in a disk drive and moves the sliding shutter to the open position when the magnetic disk cartridge is loaded into the drive. A second cutaway portion is formed in the front edge portion of the casing in a position substantially symmetrical to the position of the first cutaway portion about the centerline of the casing which is perpendicular to the front edge of the casing.

Abstract: A flexible magnetic disk is provided with a protective layer at the peripheral edge portion of the circular hole in the center of a magnetic disk sheet. The protective layer is formed by applying a radiation-polymerizable composition to the peripheral edge portion of the circular hole in the center of the magnetic disk sheet by letterpress printing, and exposing the composition to a radiation to cure the composition.