Abstract: An improved system and method is provided for enhanced add-compare-select (ACS) implementation which is particularly adapted to time-nesting or over-lapping of the time offsets for add and compare operations. The compare operation is implemented as a sequential bottom-up procedure whereby two numerical quantities are compared by first declaring one of the quantities as a "contingent" smaller or larger quantity. Subsequently, the least significant bits LSBs of the quantities are compared and the earlier contingent designation is retained unless the smaller of the compared bits is found to correspond to the quantity not previously designated as the "contingent" smaller quantity, whereupon the "contingent" designation is transferred to the previously un-designated quantity corresponding to the smaller of the compared bits.

Abstract: A disk drive system which has a plurality of disks and a plurality of transducing head positioning across. The arms are mounted about common shaft for independent notation to desired radial position on the disk.

Abstract: A disk drive system provides all required synchronization, positioning, validation, and data functions within each disk sector. All of these functions are provided within two zones, a header section and a data section. The header section includes a preamble, a synchronization character and an address field, as well as servo information for track following. The data section of each sector includes a data preamble, a data synchronization character, a bad sector bit map, the data and data redundancy information. The header section of at least one sector in a track includes a short DC-erase field, a transitionless segment which is used in synchronization. To synchronize a read/write head to the disk, the system first detects the DC-erase field. The system next searches for the header premable and synchronization character. If it finds them within predetermined times, it then looks for a valid sector address to complete the synchronization.

Abstract: A balance-moment head positioner includes a rotor assembly which rotates about a central shaft. The rotor assembly supports at the same axial location a current-carrying coil, arms for the heads, and a counterweight such that the positioner is dynamically balanced with its center of gravity at the center of rotation. The coils are arranged with legs parallel to the central shaft on diametrically opposite sides of the assembly. In addition, the positioner includes magnets and an elongated U-shaped magnetic pole member with ends facing the coils at the same axial location at the arms. Thus the torque developed when current flows through the coil, and a reactive counter-torque developed by the rotating mass coincide, substantially eliminating all torsion in the shaft, and there is no net force on the shaft.

Abstract: A data demodulator assigns a binary value to the signal recorded in a transition cell based on the amplitude of the signal in the transition cell, the amplitudes of the signal in adjacent transition cells and system experience in categorizing how recording non-linearities and system noise effect the signals. The demodulator samples a selected number of times the recorded signal in the transition cell for which a binary value is to be determined and the recorded signal in a selected number of transition cells adjacent to that cell. It then converts the amplitude of each of the signal samples to a digital symbol. Next, it concatenates portions of the digital symbols to form an interpretation word. It uses this word to enter a stored lookup table which contains binary values, and assigns to the transition cell signal the binary value associated with the word.

Abstract: A magnetic tachometer for generating a signal as a function of the velocity of a transducer positioning arm in a disk drive. The tachometer is formed by a pair of fixed parallel coils separated by a distance sufficient to allow a magnet, attached to a counterbalance portion of the rotary positioning arm, to move therebetween and thus to generate a voltage as a function of the velocity of the magnet. The coils are each wound over a thin armature member which is saturated by the magnet's magnetic field and they are differentially coupled to produce common mode rejection.

Abstract: An error detecting and correcting system implementing the Reed-Solomon (1023, 1006) code having code words whose symbols are elements in the Galois field GF(2.sup.10) generated by either the primitive polynomial x.sup.10 +x.sup.3 +1 or x.sup.10 +x.sup.7 +1. An original data word is encoded to produce a code word w(x) including a first set of checksum symbols appended thereto. Upon retrieval, the data symbols of the receive code word y(x) are encoded by the same encoder that encodes the original data word to produce a second set of checksum symbols. Both sets of checksum symbols are modulo-two summed to produce a residue R(x) from which error syndromes S.sub.i can be computed and thus enable rapid correction of errors in the received code word y(x). The system also monitors the number of non-zero symbols in the residue R(x) in order to avoid unnecessary computation of error syndromes S.sub.

Abstract: A housing (1-10) for a disk (1-12) used in a "Winchester"-type disk mass information storage unit in a data processing system. The housing is symmetrical about the plane of the disk, and supports the disk spindle (2-33) on both sides of the disk. The housing includes two substantially identical members (1-16, 17) fitted together in a clamshell-type arrangement. The housing includes a housing extension (1-26) for receiving and supporting the read/write heads (1-14) and actuator (1-15) therefor from both ends thereof. The members forming the housing are preferably thin walled castings, and may include fins (1-104) to dissipate heat or to enhance the housing's mechanical rigidity.

Abstract: A rotary actuator assembly for positioning read/write heads in disk drive mass storage systems. The actuator assembly includes an actuator motor and one or more actuator arms secured thereto. The motor provides rotary motion of the arms, to move the heads. The stator magnet of the motor is an electromagnet wound on an arcuate core; a pair of elongate permanent magnets are attached to the rotor member, for coaction with the stator magnet. The rotor member has a U-shaped cross sectional area in a plane perpendicular to its axis of rotation; the permanent magnets are fixed to the outside, bottom corners of the U and the actuator arms are mounted across the open end of the U. The rotor is of a very small radius, to minimize inertia. The permanent magnets have a flat face facing the stator, with a channel running longitudinally down the middle, to minimize flux density variations in the permanent magnet-coil gap. The rotor balances the arm relative to the rotor's axis.