Abstract: A client/server-based secure timekeeping computer system is provided. A secure-time server which is located in a physically trusted environment, includes a highly accurate time-of-day (TOD) clock, along with a key storage area containing a table of public/private key pairs corresponding to clients in the client/server network. The server encrypts a current time value from its TOD clock using a private key corresponding to a selected client. The encrypted time value is then sent to the client over an open communications channel. Each client in the network is equipped with its own secure timekeeping facility housed within the secure boundaries of a single, tamper-proof VLSI chip. Upon receipt of a secure-time transmission, a client uses its own copy of its private key to decrypt the time value, then loads the decrypted time value into its TOD clock.

Abstract: A data recording disk file with a fixed block architecture sector format that eliminates the ID region. The servo region contains sector identification information in the form of a start-of-track indicating mark recorded in a selected sector of each track and a start-of-sector indicating mark recorded in each sector. A full track number identifier is encoded in the position field within the servo region of each sector. A look-up table is built at format time to map bad sectors out of the disk file. The table contains entries for each cluster of contiguous bad sectors, and is searched at runtime to provide conversion of logical sector location identifiers to physical sector location identifiers.

Abstract: A system is provided for generating transition effects for use on a visual display. The system includes a binary table for describing a transition effect and a method for ordering the rows in the table to produce the transition. The table includes an arbitrary number of rows, each row representing a cell (group of picture elements) on the display. A numerical value, based on any function of cell location, is associated with each cell. The table is then sorted according to the numerical values. Each row in the sorted table drives a step in the transition effect. The cells described by the various rows are changed in sorted order to display the material from the image being transitioned-to. The sequence of processing of the rows causes the desired transition effect. By varying the function used to order the rows, an infinite variety of transition effects can be created.

Abstract: A technique for organizing graphical objects in a graphics database that facilitates the rapid selection of one or more graphical objects on a computer display screen. Graphical objects are stored in the graphics database using a spatially organized data structure. The spacially organized data structure is formed by recursively subdividing the graphics space until each subspace contains no more than a predetermined number of graphical objects. The spacially organized database is ideally suited for spacial queries required to select, based on visual criteria, graphical objects appearing on a display screen. Graphical objects may be selected in response to a cursor moving about a display screen under programmer control, or in response to a system request to identify one or more objects spacially located in a given portion of the graphics space.

Abstract: An optical measurement system for use in a data recording disk drive includes wavefront reconstruction optics which correct and compensate for aberrations in laser beams reflected from radial and linear diffraction gratings. The reconstruction optics include two spherical lenses and two reflectors, one of each positioned on each side of a diffraction grating. Light directed from a laser beam toward the grating diffracts into a +1 order component directed at the first set of reconstruction optics and into a -1 order component directed at the second set of reconstruction optics. The reconstruction optics compensate for the variable yaw angle caused by a linear grating and for the optical wavefront aberrations caused by a radial grating.

Abstract: A data recording disk file is provided with a fixed block architecture sector format that eliminates the ID region. The servo region contains sector identification information in the form of a start-of-track indicating mark recorded in a selected sector of each track and a start-of-sector indicating mark recorded in each sector. A full track number identifier is encoded in the position field within the servo region of each sector. A look-up table is built at format time to map bad sectors out of the disk file. The table contains entries for each cluster of contiguous bad sectors, and is searched at runtime to provide conversion of logical sector location identifiers to physical sector location identifiers.

Abstract: A data storage and retrieval system is provided which has extremely high capacity. The system includes a large array of small disk files, and three storage managers for controlling the allocation of data to the array, access to data, and the power status of disk files within the array. The allocation manager chooses the disk files upon which incoming data is written based on the current state of the disk files (active or inactive), the available capacity, and the type of protection desired (i.e unprotected, RAID), mirrored, etc.). The access manager interprets incoming read requests to determine the location of the stored data. The power manager sequences disk files between active and inactive to provide the storage requested by the access and allocation managers.

Abstract: A computer-based multimedia presentation system is provided with a synchronization scheme for recording and playing independent media. The disclosed system and method allows media processes and single medium processes to achieve and maintain synchronization with each other without process interdependence and without interprocess communication. This capability is provided by assigning a common clock for all processes, requiring all participating media processes to reference the common clock, informing each process of, a synchronization basepoint called a "zero-time", and then allowing each process to independently synchronize itself to the common clock. The common clock itself does not provide any stimulus to a media process; it is a passive component in the synchronization. The media process is the active component, referring to the common clock as required to maintain synchronization for the particular media it is handling.

Abstract: A computer system generates transition effects for use on a visual display. The system includes a binary table for describing a transition effect and a method for ordering the rows in the table to produce the transition. The table includes an arbitrary number of rows, each row representing a cell (group of picture elements) on the display. A numerical value, based on any function of cell location, is associated with each cell. The table is then sorted according to the numerical values. Each row in the sorted table drives a step in the transition effect. The cells described by the various rows are changed in sorted order to display the material from the image being transitioned-to. The sequence of processing of the rows causes the desired transition effect. By varying the function used to order the rows, an infinite variety of transition effects can be created.

Abstract: A data recording disk file is provided with fixed block address head positioning information that is readable off-track with no increase in error rate. The positioning information includes both identification information to provide radial and/or circumferential orientation for the recording head, and error handling information to ensure that the id information is properly read. Either or both of the id information and the error handling information for adjacent tracks are placed on the data storage disk at circumferentially offset positions to eliminate adjacent track interference, and at radially overlapped positions extending into the adjacent tracks to provide full readability when the head is off-track.

Abstract: A computer-based system and method is provided for positioning a cutter tool to an edge of a solid model in a computer aided manufacturing environment. A shortest distance and direction required to position the machine tool cutter to the edge of the solid model is determined. Edges are defined as three dimensional space curves. The machine tool cutter is defined as a convex envelope. Using the space curve definition, the cutter location, and the center axis of rotation for the cutter, computations are executed to determine a directional vector and distance such that moving the cutter along the vector for the prescribed distance will cause it to be in contact with the curve. Adjustments are available which cause the cutter to travel to offsets from the curve, including aligning the front of the cutter to the curve, the end of the cutter on the curve, or the back of the cutter past the curve.

Abstract: A method and device for use in measurement and compensation of nonlinear bitshift in nonlinear communication media such as magnetic and optical recording devices. The method and device are based on special bit patterns constructed to eliminate at least one harmonic of the fundamental frequency of the data pattern if all bits are communicated without any nonlinear bitshift. The presence of nonlinear bitshift is manifested by the appearance of the harmonic. By measuring the magnitude of the harmonic, the amount of nonlinear bitshift is determined, and compensation adjustment is then used to offset its effect on the data detection scheme.

Abstract: A method for measuring pulse distortion in a digital logic design. A digital logic block of interest is divided into its component primary logic functions. The pulse width distortion characteristics are determined for each primary logic function. The pulse width distortion characteristics are used to develop values representing the minimum pulse width required to guarantee full pulse amplitude propagation through each primary logic function. Thus, pulse distortion is characterized in terms of both width and amplitude components. Pulse width distortion for the entire logic block is then determined by following each logic path through the logic block and statistically summing the pulse width distortion characteristics for each occurrence of each primary logic function in the logic path.

Abstract: A rotary actuator data recording disk file is provided with a retro-reflective diffraction grating for use in measuring the angular position of the rotary actuator arm. The diffraction grating has a diffraction pattern whose pitch varies along the length of the diffraction grating. The variation in pitch is arranged such that, as the rotary actuator arm swings about its pivot axis and the diffraction grating moves across an incident light beam and simultaneously rotates with respect to it, the diffracted beam travels back along the incident path. Thus, the source and detector of a laser position measurement system can remain fixed while measuring the position of a rotary actuator arm to which the diffraction grating is affixed.

Abstract: A magetic recording system includes a current-tapering circuit which gradually reduces the WRITE current in a magnetic recording head to zero over a time interval on the same order of magnitude as the characteristic relaxation time of the domain patterns in the magnetic recording head, rather than abruptly. Specific embodiments of the current-tapering circuit create a down-sloping ramp, a decaying exponential curve, and a high-frequency burst. The resultant magnetic recording system has reduced Barkhausen noise and reproducible READ performance as well as improved READ sensitivity following a WRITE operation.

Abstract: A fully differential operational amplifier having unity gain is provided. The amplifier includes a differential input stage having two pairs of differential inputs. One pair receives the input signal. The other pair is connected internally to receive differential mode feedback from the output stage. The two pairs of differential inputs are combined with a common mode feedback signal and cascoded to the output. The amplifier incorporates automatic internal noise cancellation due to its differential mode feedback, and may be constructed in MOS logic, or in BiCMOS for high frequency operation. Applications include buffering for filters in circuitry requiring high speed and noise cancellation, such as data channels and servo channels in data recording devices.