Abstract: Techniques and devices based on second surface optical recording using thermomagentic writing in a magneto-optic recording layer and first surface magnetic reading of written data in the recording layer.

Abstract: The invention provides a system for wireless transmission of data, including position data. The system includes a hand held digital computer, a position-locating device providing position information to the digital computer and a VHF and/or UHF radio frequency transmitter. A radio modem, having an input for digital data from the hand held digital computer and an output connected to the transmitter, includes a modulator for converting digital data from the computer into a modulated analogue RF signal for transmission.

Abstract: An optical disk drive having a thermal control mechanism on the optical head to control the spacing between the optical head and the surface of the storage medium.

Abstract: A closed loop head positioning servo system is disclosed for use in a disk drive employing a disk pack having a dedicated servo surface and a number of data surfaces carrying both data and servo information. A track counting coarse positioning system is used to move the heads in a ganged assembly to the vicinity of a desired cylinder. A fine positioning system includes one error circuit for generating an error signal representing the deviation of a servo head from a desired cylinder on the dedicated servo surface. Another error circuit generates a second error signal representing the offset of a selected data head from a selected data track in the same cylinder. Analog circuits combine the error signals to produce an output signal which, when applied to an actuator, centers the selected data head on the selected track.