Disc storage cassettes comprising index features

A disc cassette comprising:

• a curved portion including multiple ribs, wherein the ribs define multiple disc slots in the curved portion that are configured to hold multiple discs in place, and the discs are spaced apart by the ribs;
• and
• multiple index features positioned on an inside edge of the curved portion, wherein edges of the index features are aligned with centers of the disc slots, and the index features are configured to allow alignment of a kicker device of a disc retrieval unit (DRU) to a disc of the disc cassette to lift the disc into a disc gripper device without disturbing one or more other discs of the disc cassette that are adjacent to the disc.