 The end of a file was designated by a special recorded pattern called a tape mark, and end of the recorded data on a tape by two successive tape marks.The physical beginning and end of usable tape was indicated by reflective adhesive strips of aluminum foil placed on the back side.Effective density also increased as the interblock gap (inter-record gap) decreased from a nominal 0.75-inch on seven-track tape reel to a nominal 0.30-inches on a 6250 bpi nine track tape reel.