International Business Machines Corporation

Peter Thomas Marino

Otto Richard Buhler

Frank B Shelledy

Edmond W Smathers

Homer J Gardner

Joseph Philip Baca

A system for reading information stored on a flexible magnetic disk is disclosed. The system involves an amplitude detector for detecting at predetermined times whether the amplitude of the read signal is positive, zero or negative. This system includes an amplifier for the differential raw data signal whose gain is variable in response to changes in the amplitude of the raw data signal which occur over a relatively long period. The output of the automatic gain control amplifier is an equalized differential signal applied to the detector and to a threshold generator which provides an output reference signal which is a predetermined percentage of the input signal, and which is capable of following relatively rapid changes in the amplitude of the input signal. A positive and negative comparator circuit continually compares the differential equalized data signal against the generated threshold reference signal. The outputs of these comparators are sampled at clock times established from a phase-locked loop which is synchronized by pulses derived from the peaks of the input data signal.

Amplitude sensitive three-level detector for derivative read back

A magnetic head assembly for cooperating with a relatively moving medium, on which servo information and data information is recorded, and for reading and/or writing on said medium and for erasing said medium is fabricated so that the effect of pickup interference or unwanted signals during playback is reduced. The magnetic head assembly incorporates a geometry which shifts the signal envelope of the interfering signal so that it is in phase with the signal envelope of the desired signal. The preferred geometry is to dimension the head core so that the distance between two gaps or between a single gap and the edge of the core is equal to the distance between the servo tracks on said medium. Additionally, the gap of the head has a gap null occurring at the frequency of the interfering signal.

Minor bit reduction on a magnetic head

A servo sector record track location pattern provides both seeking and following capability. The durations of servo signals within a servo sector uniquely identify track location lines within a band of such track location lines. A first-appearing servo signal pattern always provides full amplitude readback signals for normalizing track following operations. Subsequently appearing servo signal patterns yield an amplitude representative of energy content which is comparable with the signal amplitude and energy content of the first-appearing servo signal for yielding track position error signals. Apparatus for employing the novel servo pattern is also disclosed.

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Boulder, CO, United States of America

Peter Thomas Marino