Described is an optical data storage system which comprises a multiple data surface medium (12) and optical head. The medium comprises a plurality of substrates (50,56,62,68) separated by a light transmissive medium. Data surfaces are located on the substrate surfaces which lie adjacent a light transmissive medium. The data surfaces are substantially light transmissive. At least one of the data surfaces includes information identifying the type of tracking marks contained in at least one data surface.