The present invention relates to a data storage device comprising a circular disc (30), a data storage medium on at least one surface of the disc, a spiral track extending within the storage medium about the axis of the disc, and a plurality of data storage sectors formed on the track. According to the invention the storage device is characterised in that the storage medium is formed with a reference mark (100) extending radially from the axis of the disc, and the data storage sectors are arranged in groups extending along the spiral track, one end of each group of sectors being located adjacent to one of the points of intersection of the reference mark with the spiral track.