Abstract: Easily-fabricated, high track density, size-tolerant and efficient sector servo patterns are provided for optical disks. Easily-fabricated and efficient codes are provided for use with sector tracking optical disk servo systems. Marks larger than the spot size are used to avoid resolution problems and the limits of photolithographic processes. Independence from line-width variations is achieved by balancing. The features used for servo information are in every case in the form of pits or depressions in the substrate surface, such as could be produced by exposing a photoresist through a mask, followed by etching. The servo detectors sense the changes in reflectance from the disk owing to the cancellation of light waves from the two differing depths. The optimum depth is one-quarter wavelength in the substrate, so that the contributions from the two depths will be exactly out of phase. This produces maximum signal, but it also means that no data can be expected to be written or read in the servo sectors.

Abstract: A track following servo system for a magnetic disk file employs a buried servo pattern having two types of signals therein. The first is a reference signal of frequency f and the second type are control signals of frequency 2f, adjacent control signals being 180.degree. out of phase with each other.

Abstract: A single-gap transducer simultaneously senses recorded control or servo signals and record data signals. A magnetic medium used with this invention is preferably a single layer magnetic medium. The head gap length and pole-tip face length allow different portions of the pole pieces in a magnetic transducer to be utilized during the simultaneous read and record operations. The servo signals are preferably deep and hard recorded into the layer whereas the data signals are preferably pulse width limited and recorded adjacent the surface portion of the magnetic layer.

Abstract: A short duration pulse is recorded for each transition of a data bit stream. Such short duration pulses are AC bias recorded for enhancing recorder operations. The recording is preferably used with a buried control signal; the system enables simultaneous recording of data with reading or sensing the control signals. Specific equalization and detection techniques are disclosed. A DC restoring detector, operating synchronously to a detected bit stream, continually adapts its operation to readback signal amplitude variations. Because of high frequency aspects, the circuit elements can be mounted immediately adjacent a transducer or as close thereto as possible.

Abstract: A first signal to be stabilized in a magnetic record member is recorded via a head having a given maximal gap length and pole pieces of high saturation induction. After the first signal is recorded, the magnetic record member is surface erased for stabilizing the just recorded signal. In a preferred form, the surface erasing is performed by AC erasing via a transducer having a gap length less than said maximal gap length. The pole pieces of the erasing head need not have the high saturation induction of the first mentioned head. After such stabilization, signals can be easily recorded and recovered from the magnetic record member by using transducers with gap lengths less than such given maximal gap length and using the normal ferrite heads having a lower saturation induction than the first mentioned heads. The first signal can be advantageously employed as a position indicating signal in a magnetic record member, such as a storage disk or tape.