Abstract: In a method of recording, in the over-write mode, bivalent signals "0" and "1" on an opto-magnetic record medium having a ferrimagnetic material whose compensation temperature is higher than a room temperature, but is lower than a Curie temperature, an external magnetic field is applied to the record medium, and a laser light beam is modulated in accordance with the bivalent signals. When the bivalent signal "0" is to be recorded, the laser light beam is set to a lower power level and the ferrimagnetic material of the record medium is heated to a temperature higher than the room temperature, but lower than the compensation temperature so that the ferrimagnetic material is magnetized in the same direction as the external magnetic field.

Abstract: An optical disc consists of a base plate, a reflective thin layer and a protective thin layer. As the base plate, polymethylmethacrylate is used. Since defects in the protective thin layer are a function of defects in the base plate, in order to reduce defects in the protective thin layer, defects in the base plate are reduced. For reducing defects in the base plate, a copolymer of methyl methacrylate and methyl acrylate is used.

Abstract: Optical data storage media of various technologies, particularly those with multiple layers of varying absorptivities of light include at least one polymer layer and a metal reflective layer. The metal reflective layer is constructed of an elemental metal or metal alloy having the desired reflective properties and which also softens or melts or both at, near or below the temperature reached by the polymer layer during recordation.

Abstract: A CD system in which position information of different pieces recorded on the CD is used to calculate how many of the pieces can be recorded on one side of a tape. When the maximum number of recordable pieces have been played, the tape is reversed. The invention also allows the pieces to be evenly divided between the two sides of the tape.

Abstract: A method for recording and reproducing information on or from an optical recording medium, which comprises:recording information by illuminating light to the optical recording medium which is equipped as a recording film with a thin film comprising dispersed fine grains of a material capable of showing a metal-insulator transition to cause the metal-insulator transition owing to the heating effect of the light; and reproducing the information by utilizing changes in optical characteristics owing to a plasma resonance absorption by the fine grains dispersed in the thin film. The method of this invention permits high-density recording with high sensitivity and upon reproduction, enables reproduction of record with a high signal/noise ratio. The recording medium obtained by this method is an erasable optical recording medium, which permits its reutilization for recording and reproduction after erasure of the previously-stored record.