Abstract: A method and system for developing continuous position control signals for continuously repositioning a data head relative to an addressed data track on a rotating magnetic disk. The method includes the steps of formatting the disk with a unique servo pattern to provide servo signals having servo frequencies F1 and F2, which correspond to spectral nulls in the frequency spectrum of the encoded data stored on the disks. The method further establishes addressable data track locations related to the servo pattern which have a nominal width corresponding to the width of one servo band of the pattern. After positioning the data head to a data track the method involves "side" reading with the data head the servo pattern that is adjacent both sides of the data track to develop the positional control signals as data encoded with spectral nulls at F1 and F2 is transferred to and from the disk.

Abstract: A magnetoreristive head assembly has a magnetic bias level control for continuous compensation of thermal, stray field and stress fluctuations, as well as other types of fluctuations. The magnetoresistive head assembly includes a magnetoresistive element for sensing signals recorded on a magnetic medium, and for generating electrical signals corresponding to the recorded signals. A bias current balancing circuit has an input connected to the magnetoresistive element for sensing the electrical signals and for generating a correction bias current therefrom. A feedback correction circuit converts the correction bias current into a correction magnetic bias field and applies the field to the magnetoresistive element to limit the shifting of a current bias point of the magnetoresistive element and to compensate for bias fluctuations.

Abstract: A magnetic thin film head with reduced undershoot characteristics includes a pair of relatively high permeability pole members having a low permeability gap member therebetween. Disposed adjacent to the surfaces of the pole members, which are opposite to the gap member, are layers of magnetic material of lower permeability than the permeability of the pole members, these lower permeability layers having a Curie point temperature which is within the operating temperature range of the head so that these lower permeability layers are paramagnetic. In operation, the lower permeability layers provide a change in permeability across the head gap which reduces the transition in permeability at the head pole tips, thereby reducing undershoots.

Abstract: A magnetic head is formed by depositing a pad pattern on a substrate with a flat upper surface. The pad pattern includes two spaced inner slopes that face each other. An air bearing surface plane is defined between the inner slopes where the air bearing surface of the magnetic head is to be formed. An undercoat layer is deposited on the pad pattern, such that the undercoat layer follows the contour of the inner slopes to form a recessed region between the inner slopes. A magnetic layer is deposited on the undercoat layer to form a first pole P1 that follows the contours of the inner slopes. A gap layer is then formed on top of the first pole P1 and follows its contour. Conductive coils are formed within the recessed region. A second magnetic layer is deposited over the coils and gap layer to form a second pole P2. The magnetic head is lapped at the air bearing surface plane to form the final air bearing surface.

Abstract: A test disk is used to measure disk drive alignment and other parameters without removing the drive from its computer system and without any need for special test equipment. It includes a pair of prerecorded signal tracks separated by a gap smaller than the width of the head so that one track is used for providing computer readable signals and the other is used to inject variable interference into the composite signal under the head. Multiple pairs of tracks at differing radii are included for measuring drive alignment and other parameters. The method for measuring alignment and other parameters suppresses measurement errors due to disk signal modulation and changes in track radius. Alignment testing requires only a single measurement and is capable of resolving the measurement to the nearest bit so that maximum accuracy is achieved.

Abstract: A copy protected magnetic storage disk includes a plurality of record tracks suitable for recording information-bearing data accompanied by a clock signal having a signal strength corresponding to the signal strength of the data. At least one of the record tracks includes a recording pattern representative of a code burst derived by temporarily changing the clock signal during a recording operation. Upon playback, the recording pattern of the code burst causes a random series of playback data to be produced which are dissimilar from one playback operation to the next playback operation. To verify the status of a disk (original or a copy), the code burst is read twice. With an original disk, the playback data is dissimilar; each time a copy is read, however, the same playback data is produced.

Abstract: A fluid level indicating apparatus includes a piston and cylinder assembly which is located adjacent the surface of a body of fluid contained within fluid reservoir and includes openings to admit such fluid thereinto with the piston in one extreme axial position, and to vent air from the cylinder but restrict fluid flow therefrom during movement of the piston from the extreme axial position. The piston is connected by a link to a pivotally mounted level indicating plate which pivots in conjunction with pivotal movement of an actuator element (e.g. the hinged cap of the fluid reservoir closure) to a position indicating the level of fluid in the reservoir. The actuator element is releasably connected to the indicator plate in a manner to cooperate with the restriction of fluid flow from the cylinder upon piston movement to position the indicator plate at an appropriate level indicating position for any given fluid level within the indicating range of the apparatus.

Abstract: A low fluid level warning system (100) is adapted for use with a conventional oil circulation and low pressure warning system in an engine-driven vehicle. Oil from a crankcase reservoir (102) is pumped through an inlet conduit (110) to varius engine supply lines (116). A portion of the oil is also pumped into an enclosed chamber (124). A pressure sensor diaphragm (132) and switch contacts (130) sense the chamber pressure and illuminate a warning lamp (142) when the pressure is below a predetermined pressure. A drain conduit (160) extends from the bottom of the chamber at the bottom of the oil reservoir (102). A vent conduit (150) extends from the top of the chamber to a predetermined level in the reservoir (102). If the oil in the reservoir (102) is below the predetermined level, the chamber (124) drains completely when the engine is turned off. If the oil in the reservoir (102) is above the predetermined level, the chamber oil does not drain.

Abstract: A magnetic disk includes a pair of azimuth test tracks of relatively narrow trackwise width located adjacent each other so that a magnetic head, the azimuth of which is to be measured, straddles both tracks at the same time. Each test track includes a recording pattern comprising a series of separate, uniformly spaced magnetic domains of alternating orientation, the recording pattern on one track being in a particular phase relative to the recording pattern on the other track. Upon playback, the magnetic head produces a composite playback signal comprising a series of localized peaks, the time between adjacent peaks being functionally related to head azimuth.

Abstract: An alignment testing device comprising a magnetic media with data tracks in nonstandard locations with bidirectionally progressive degrees of misalignment for testing the alignment of the transducer head in a magnetic storage device such as a floppy disk drive. The alignment testing device allows the user to determine the boundaries of track alignments that the transducer head can read, and thereby determine any discrepancy between the heads actual alignment and correct alignment.

Abstract: A multiple system data storage disk adapted for use with more than one type of computer. The disk is specially formatted to include software for each computer. The disk includes four discrete recognition headers, one for each target computer, placed at locations on the disk where each computer expects to being its data loading operation. Each header further includes software directing the computer to step out to a discrete group of data tracks located elsewhere on the disk. Each data track group contains an identical program, written in each target computer's language. The disk is suited to video games for multiple computers. An alternative embodiment of the disk includes a header or headers containing a magnetic signature for copy protection. A disk can be produced with twenty-four such headers, one for each type of computer on the market, which can be mass produced to provide low-cost copy protection for all machines.