OPTICALLY READABLE STORAGE DISC

摘要

An interchangeable optically readable storage disc comprises two flat transparent substrates (21, 23) which are secured to and spaced from each other by annular means (24; 25). The circumferences of the substrates are protected against damage by the use of circumferential means (27) which are also employed for balancing purposes, for example by securing balancing mass (28) to these means.