Combination optical data medium with multiple data surfaces and cassette therefor

Claim 1

A combination comprising: a cassette and an optical data medium in said cassette and from which information recorded on a data surface thereof is reproduced by focusing a laser beam thereon and reading the light reflected from the data surface, said medium comprising: a first transparent layer having a first and a second surface, said second surface being a first data surface; a semi-transparent layer on said second surface; a second transparent layer having a third and a fourth surface, said third surface being in contact with said semi-transparent layer and said fourth surface being a second data surface; and a reflection layer on said fourth surface; and; said cassette comprising: a casing in which said medium is contained and having an opening therein which is normally open and through which the laser beam is directed onto said medium; and a transparent plate movably mounted on said casing for movement between a first position at which the transparent plate is at a position other than over said opening and a second position in which said transparent plate is over said opening, said transparent plate having a thickness for causing a laser beam directed through said opening onto the medium to be focused on one of said second and fourth surfaces with the laser beam focused on the other of said second and fourth surfaces when said transparent plate is not over said opening, and said first surface of said medium being exposed through said opening.