Abstract: A method for overwriting information in a magneto-optical memory medium which includes a simultaneous writing and erasing step of continuously irradiating a written information-carrying area of the recording layer of the memory medium with two different pulses from a single laser beam head in accordance with information to be written, regardless of the presence or absence of written information. A variation includes irradiating the written information-carrying area with an erasing pulse from a laser beam head, regardless of the presence or absence of written information, and then selectively irradiating the information-erased area with a writing pulse from another laser beam head in accordance with information to be written. According to these methods, it becomes possible to carry out a simple and high-speed overwriting with an increased and stabilized bit positioning accuracy.

Abstract: A method of overwriting information in a magneto-optical memory medium which includes a simultaneous writing and erasing step of continuously irradiating a written information-carrying area of the recording layer of the memory medium with two different pulses from a single laser beam head in accordance with information to be written, regardless of the presence or absence of written information. A variation includes irradiating the written information-carrying area with an erasing pulse from a laser beam head, regardless of the presence or absence of written information, and the then selectively irradiating the information-erased area with a writing pulse from another laser beam head in accordance with information to be written. According to these methods, it becomes possible to carry out a simple and high-speed overwriting with an increased and stabilized bit positioning accuracy.

Abstract: An optical writing and reading method and apparatus for writing data on a recording medium. To prevent an over-writing of data, a mark is written to indicate that data is already written. Before writing data, a mark is written on a mark recording region. Simultaneously with the writing of the mark, the light quantity reflected from the mark recording region is detected. When the reflected light quantity indicates that data is already written, subsequent data writing is inhibited.

Abstract: A magnetic disk storage apparatus having a servo disk and a servo transducer cooperating therewith is described. The servo disk is provided with a magnetically pre-recorded concentric arrangement comprising of an inner guard zone, a servo track zone, and an outer guard zone. The servo track zone provides information regarding both the moving speed and the position of the servo transducer; while at least one of the inner or outer guard zones provides information regarding both the moving speed and the guard zone of the servo transducer.

Abstract: An electromagnetic actuator for linear driving of movable heads of a magnetic disc unit in an information processing system. A plurality of slits or plates are provided with a magnetic pole inscribed directly on the internal surface of a permanent magnet, and increase magnetic reluctance of the magnetic path and reduce inductance of a moving coil, thus providing shorter positioning time and stable control. In order to obtain the constant strength of magnetic flux and/or torque of a moving coil, said slits or plates have a particular structure.