North American Philips Corporation

Sperry Rand Corporation

Donald T Best

Juan M Gottschalk

Richard C Carickhoff

Alvin Schultz

A magnetic head having a fixed gap length (g.sub.n) can be compensated to simulate a head with a larger gap length. This magnetic head is adapted to read alternate magnetic media recorded with at least a selected one (x) of a plurality of wavelengths, to produce a head signal. A compensator has a transfer circuit and a disabling device. The transfer circuit is coupled to and driven by the magnetic head to produce a compensated signal that is a function of x, for simulating another gap length (g.sub.1) different from the fixed gap length. The disabling device is coupled to the transfer circuit for selectively preventing simulation of a different gap length.

Magnetic head compensator

For identifying a preamble or other pattern in a binary bit stream, containing data coded to have a different average number of ones to zeroes from the pattern in question, a pattern detection circuit includes a shift register, a unitary adder and a comparison circuit. The shift register has a sufficient length that there is at least a high probability that the number of ones stored therein is different for the pattern in question from the range of number of ones found in that length of the data stream. The unitary adder counts the number of ones in the register, and this value is compared with the range of values which that length of the pattern should contain. If the pattern to be detected is a preamble used for bit synchronization, and the data are coded in a way which may lead to possibility of synchronization to a subharmonic, a ones-average detector may be used to disable the synchronization circuit for a local clock until the preamble is detected. For modest length preambles, there still should be sufficient length to synchronize the clock after preamble detection.

Pattern detection and synchronization circuit

The magnetic head assembly can read from and write to a plurality of tracks on a magnetic medium. The medium and assembly are relatively movable in a longitudinal direction. The assembly includes a plurality of pairs of reading poles. The assembly also includes a plurality of pairs of read loops, each adjacent and magnetically coupled to an associated pair of said reading poles. Also provided is a plurality of writing poles. Each pair of said writing poles is aligned with a different corresponding one of said writing poles. The assembly also includes a plurality of pairs of write loops, each pair of write loops being adjacent and magnetically coupled to an affiliated one of said writing poles. Each pair of write loops is selectively driveable with a pair of currents in either the same or opposite sense.

Compatible magnetic head assembly

In a magnetic recording system having a medium for storing information in the form of encoded digital data, an improvement in the recording head control circuit including means and a method for determining the temporal occurrence of a major write transition of the encoded digital data and producing a minor write pre-transition and a minor write post-transition each having a lower amplitude and an opposite direction to that of the major write transition thereby providing a readout pulse corresponding to the combined write transitions having a narrower pulse width and improved symmetry which enhances the accuracy in reading out the recorded digital data and increases the packing density in the storage medium of the recording system.

Precedent and subsequent minor transitions to alleviate pulse crowding

A magnetic read/record head having a layer of uniaxially anisotropic magnetic material as the pole faces, which increases the ratio of magnetic reluctance between the pole faces to the magnetic reluctance along the fringing flux path through the recording medium. Two embodiments of the invention are disclosed, one embodiment providing a layer of anisotropic magnetic material in a continuous layer around a complete loop from one pole face to the other pole face, and the other embodiment providing a layer of anisotropic magnetic material confined to each of the pole regions.

Magnetic transducer

The invention pertains to an optical scanning technique which is capable of reading and accepting a wide range of out-of-tolerance symbols. The technique provides that if a successful scan occurs, the signal circuits maintain a status that indicates a true signal is being processed. However, if an unsuccessful scan takes place the signal circuits introduce a distortion therein in order that the symbol may be read successfully.

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Lafayette Hill, PA, United States of America

Donald T Best