Abstract: A computer storage unit usable with DAT cassettes. The unit has a tape drive, a carriage that is movable laterally relative to the tape drive opening, and a magazine having slots sized to releasably hold the cassettes therein. The magazine is releasable attachable to the carriage. A pair of gripper arms is rotatably mounted at the end of an arm attached to a traveler which moves the gripper arms between a selected magazine slot and the tape drive opening. The gripper arms are rotatable between a grasping position, a pushing position and an open position using a solenoid-driven actuator arm which linearly moves a head block to which the gripper arms are loosely connected at a position offset from their axis of rotation. A sensor is used in conjunction with the gripper arms to selectively move the cassettes during a test cycle to determine if cassettes are present in the magazine slots and whether the cassettes are in backwards.