Abstract: A read-only optical recording disc comprising a substrate, a metal reflective layer and an overlying protective layer, at least one of the substrate and the protective layer being light-transmissive, is marked by means of a pulsed scanning laser beam which transmits light in a patterned array through a transparent layer of the medium and indelibly marks the reflective layer of the medium without disrupting the surface continuity of the substrate and protective layer.

Abstract: A rectifier and preregulator circuit using a first silicon controlled rectifier (SCR) to rectify AC voltage and apply the rectified voltage across a capacitor which is used as a storage device. The circuit also includes a transistor, zener diode and a second (SCR) in a switching arrangement for turning on the first SCR and for turning off the transistor and zener diode when a minimum voltage is reached so as to minimize dissipation of electrical power in the circuit. A second zener diode and a third SCR are used in a switching arrangement to control the maximum rectified voltage from the circuit.