FIELD: data medium, reader, and data medium, manufacture. SUBSTANCE: data medium has track with supporting structures dividing this track into areas. Supporting structures submit information related to data layout on medium. Information is presented in structures in predetermined way. Supporting structures also bear auxiliary information. The latter relates to first mentioned information and includes check information used in data processing for preventing use of unauthorized copy of data medium that does not bear auxiliary information. Reader has demodulation means for recovering auxiliary information. Mentioned auxiliary information is included in supporting structures during manufacture of data medium. EFFECT: simplified means for recovering auxiliary information preventing use of unauthorized copy of data medium. 14 cl, 7 dwg
