DOPPELSCHICHTIGES OPTISCHES DATENAUFZEICHNUNGSMEDIUM

摘要

A dual stack optical data storage medium ( 30 ) for recording and reading by means of a focused radiation beam ( 29 ) is described. The beam enters the medium ( 30 ) through a first radiation beam entrance face ( 21 ). The medium has at least a first substrate ( 1 a) with on at least one side of the first substrate ( 1 a) a first layer stack ( 2 ), comprising a first information layer ( 3 ), a second layer stack ( 5 ), comprising a second information layer ( 6 ) and a first transparent spacer layer ( 4 ) between the first layer stack ( 2 ) and the second layer stack The first layer stack ( 2 ) is present at a position closer to the first radiation beam entrance face ( 21 ) than the second layer stack ( 5 ). The first information layer ( 3 ) is one selected from the group of types consisting of a read only layer and a write once layer, and 10 the second information layer ( 6 ) is one selected from the group of types consisting of a read only layer, a write once layer and a rewritable layer. The type of the first information layer ( 3 ) is different from the type of the second information layer ( 6 ). Compatibility of the medium with read only standards is achieved while the advantages of writability and erasability are maintained. Double sided versions of the medium are also described having a 15 third and fourth layer stack ( 7, 10 ).