Abstract: A memory management unit (MMU 12, FIG. 1) is provided which allocates space in a memory unit (2, FIG. 1) to a number of user tasks being performed concurrently by a CPU (5, FIG. 1). The MMU is capable of dynamically changing the number of concurrent user tasks and the page allocation for each task. The MMU also allows direct memory accesses into the address space of any user task.

Abstract: A disk drive shock mount is provided which attenuates shocks and vibrations to a disk drive (1, FIG. 1). The mount comprises a cradle 20 which is affixed to the disk drive housing, and a mounting plate 10 which may be used to suitably secure the disk drive assembly 1 to the next higher level of assembly. Flexible, compressible vibration isolators 50 of rubber or plastic are used to couple the cradle to the mounting plate. Rigid pins 70 on the cradle mate with grommet-enclosed apertures 60, 61 in the mounting plate to limit the degrees of motion permitted between the cradle and the mounting plate.

Abstract: A pipelined digital computer processor system (10, FIG. 1) is provided comprising an instruction prefetch unit (IPU,2) for prefetching instructions and an arithmetic logic processing unit (ALPU, 4) for executing instructions. The IPU (2) has associated with it a high speed instruction cache (6), and the ALPU (4) has associated with it a high speed operand cache (8). Each cache comprises a data store (84, 94, FIG. 3) for storing frequently accessed data, and a tag store (82, 92, FIG. 3) for indicating which main memory locations are contained in the respective cache.The IPU and ALPU processing units (2, 4) may access their associated caches independently under most conditions. When the ALPU performs a write operation to main memory, it also updates the corresponding data in the operand cache and, if contained therein, in the instruction cache permitting the use of self-modifying code. The IPU does not write to either cache.

Abstract: An electronic workstation comprising a detachable keyboard (10, FIG. 1) associated with the workstation for permitting operator interface to same. The workstation comprises a base (2) with an upper surface (15) inclined towards the operator, a viewable element (8) such as a CRT screen, and a support (4,6) for supporting the viewable element relative to the base. The keyboard 10 is positionable by the operator in any of several orientations relative to the base 2. In one orientation the keyboard is fully incumbent upon the base, thereby maintaining the workstation profile or "footprint" relative to a work surface (30) at a minimum. In another orientation the keyboard rests only partially on the work surface. Protuberances (24, 34) on the upper surface of the base register with corresponding indentations in the lower surface of the keyboard to facilitate locking the keyboard in the desired position relative to the base.

Abstract: A direct memory access controller (8, FIG. 1) is provided which can service a number of input/output controllers (24, 26) concurrently on a time-division multiplexed basis. The direct memory access controller 8 (DMAC) is capable of interconnecting more than one input/output device (64, 66, 69, 74, 76) with more than one system memory (2, 20). The DMAC 8 can also transfer data from one system memory (2) to a second system memory (20), or within one system memory.

Abstract: In a system including a central processor, central memory, and local video controller communicating with a video terminal, the video terminal including a terminal processor and a video memory for storing video information for displaying on the terminal screen, a change detect circuit is provided in the local video controller for detecting whenever a change has occurred in that portion of the central memory containing video information to be displayed on the terminal's video screen. Responsive to the change detect circuit, the local video controller sends updated video information to the video memory at the terminal.The change detect circuit reduces the workload on the system by sending only the updated video information to the terminal.The change detect circuit is capable of operation with a system employing multiple terminals each having multiple independent screen display areas.

Abstract: In a video terminal comprising a terminal processor communicating with a central processor, and a single-block non-interleaved video memory for storing video information for displaying on the terminal screen, a video update FIFO buffer is provided for buffering video information between the terminal processor and the video memory. The 3-word FIFO buffer is filled during screen trace, and it transfers its contents into the video memory during screen retrace periods.The FIFO buffer permits screen information to appear without flicker. It also permits scrolling of row segment screen information by reading a row segment from the video memory, temporarily storing it, and then writing it into an adjacent row segment. It also permits flexible cursor symbols, cursor blinking of individual display screen areas, and certain data format conversions.

Abstract: In an intelligent video terminal communicating with a central processor, a video memory controller is provided which performs a variety of data transfer operations in response to commands from a terminal processor. The data transfer operations include block reads and block writes, copying an entire screen data line or a portion thereof, scrolling an entire screen line or a portion thereof, filling a screen line or a portion thereof with a desired character, and independently scrolling a row segment within each of multiple independent screen display areas. In addition, the current location of the cursor within each screen display area can be monitored.Many of the data transfer operations are performed by the video memory controller in response to a single terminal processor command, thereby minimizing terminal processor interrupts.

Abstract: A printed wiring assembly card insertion/extraction tool is provided of circular cross-section with a cam-like member at one end. Each card within the card cage has a tab centrally located along one edge, the tab containing a keyhole-like aperture. When the cards are in their normal side-by-side position within the card cage, all of the apertures line up with a similarly shaped aperture in a support bracket mounted on one side of the card cage, such that the insertion/extraction tool may be inserted through the apertures. A selected card may be extracted by appropriate rotation of the tool about its axis, whereby the cam-like member engages the corresponding aperture of the selected card and forces it out. Likewise, cards may be inserted by reversal of the process. A retaining bracket is provided on the opposite side of the card cage opening from the support bracket.