Abstract: A data storage file for use with removable media is provided with media bearing servo information indicative of its desired center of rotation. The data storage file is also provided with media locating apparatus, which prepositions the media within the data storage file prior to media rotation, and servo information decoding apparatus, which scrutinizes the servo information. As the media rotates, the servo information decoding apparatus monitors the position and behavior of the servo information on the media and so examines the distance between the actual and desired centers of rotation of the media. Should this distance prove unacceptably large, indication is given that the media should be reintroduced to the media locating apparatus before proper operation of the data storage file may take place.