Abstract: A ternary magnetic recording system wherein groups of binary input digits are transformed into corresponding groups of ternary recording code symbols utilizing a hierarchical code substitution system in which the longest valid group in the code is encoded. The code substitution system provides retention of the advantageous properties of a prior ternary recording system while significantly enhancing the automatic gain control utilized in amplitude discrimination between two of the ternary recording symbols. Anomalous detection of chained doublets is also obviated. Data recovery is effected by decoding apparatus utilizing an eight bit addressable ROM addressed with a twelve bit ternary word.

Abstract: Circuitry for distinguishing each value in a read signal magnetically recorded in ternary-3 position modulation in which the values 1, 2 and 0 are detected and equalized into a singlet, a doublet and absence of magnetic flux change. The circuitry first determines the position locations of each singlet peak and doublet crossover point to establish proper timing of the output signals and then identifies the particular type of signal appearing at the timing points in the read signal sequence. Singlets are identified by the much greater amplitudes in the integrated read signal. Doublets are identified as waveforms having slopes at zero crossovers that correspond in polarity to that of the previous singlet. A novel detector circuit is provided that can correctly identify doublets in a code sequence, irrespective of the presence of a previous singlet, when a recording rule is followed that includes the insertion of a number of consecutive ternary 0 symbols into the recorded signal.

Abstract: Apparatus and method for encoding binary data in a ternary format including ternary 0, ternary 1 and ternary 2 code symbols. In a preferred embodiment of the invention utilized for magnetic data storage, a ternary 0 is represented by the absence of signal change, a ternary 1 is represented by a single transition and a ternary 2 is represented by a pulse or pair of closely spaced transitions. Further features of the invention provide for merging ternary code symbols so as to prevent the spacing between adjacent symbols from becoming so small as to create undesirable crowding, and inserting and shifting symbols to prevent the spacing between adjacent symbols from becoming so great as to adversely affect recovery of the encoded data.

Abstract: A saturated flux equivalent to three amplitude level recording is attained by recording two levels by conventional saturation of the medium and the third level by writing a high frequency which erases old data and is read back as a zero level due to limited playback or read frequency response.

Abstract: A method and apparatus for encoding binary data in a data stream so as to increase the number of data bits represented by one transition, such as a transition recorded on a magnetic medium, and thereby increase the storage density. The data stream is converted into words each having m bits. Two of the data words are stored so as to be simultaneously accessible to a converting system that converts the data words into code words wherein each code word has n bits. In the invention, m/n=2/3. In order to increase the space between adjacent transitions, the conversion is carried out according to a scheme wherein all code words have at least one binary ONE and lack successive binary ONEs except certain cases in which a code word is converted to all ZEROs to avoid ONEs in the nth bit of a given code word and the first bit of the code word following the given code word. Also described is a decoding method and apparatus for recovering the encoded data and decoding it to the original binary data.

Abstract: A binary data encoding and recovery technique for which the encoding is carried out by separating the binary data into successive data words each containing an equivalent number of data bits, generating one or more code signals representative of each data word where each code signal corresponds to a signal change at one of a plurality of signal change positions in a data cell associated with the data word and is spaced from adjacent signal changes in the data cell by at least a prescribed minimum amount, and assuring that succeeding signal changes occurring in a sequence of data cells are spaced at least the prescribed minimum amount by determining whether a signal change in one data cell would be spaced less than the prescribed minimum amount from a signal change in an adjacent data cell and in such event providing for the code signals related to such signal changes to be merged into a code signal corresponding to a signal change positioned at the boundary of the adjacent data cells so that the prescribed mi

Abstract: A signal amplitude equalizer circuit, having linear phase, for reforming high density magnetically recorded read-back signals to remove peak shift and the resulting errors caused thereby. The equalizer circuit employs series balanced differential amplifier circuits in connection with properly terminated delay lines across the amplifier output terminals to provide an adjustable transfer function that transforms the readhead signal, that follows an exponential frequency spectra curve, into a cosine power frequency spectra curve which, in the time domain, possesses a sufficiently narrow base to eliminate peak shift and its resulting amplitude decay.

Abstract: Magnetic recording apparatus including signal equalization means for recording data so as to obtain read pulses therefrom which are symmetrical about their peak and substantially narrowed at both the base and half amplitude points whereby increased packing density may be achieved without attendant peak shift, the equalization being provided by means for generating an ac bias signal in conjunction with data transitions and associated equalizer transitions referenced to the bias signal for application to magnetic recording means.

Abstract: A dual channel signal detector circuit comprising an equalizer for responding to a variable peak amplitude input signal, in which the peaks are representative of data, so as to provide a substantially constant peak amplitude output signal having discrete data representative pulses spaced along a base line, which is substantially flat at the zero level in regions intermediate the pulses, for application to separate peak detection and amplitude detection channels. The peak detection channel produces data pulses each indicative of the relative time occurrence of the peak of a respective data representative pulse while the amplitude detection channel is triggered by signal levels of the data representative pulses exceeding a predetermined threshold to produce gating pulses for gating the data pulses to the circuit output substantially exclusive of any noise that may be present at the input of the circuit.