Abstract: A method and means within a hierarchical, demand/response DASD subsystem of the passive fault management type in which, upon the occurrence of fault, error, or erasure, a long device busy signal of finite duration is provided to a host CPU. Any DASD storage device subject to the anomaly is isolated from any host inquiry during this interval. These measures permit retry or other recovery procedures to be implemented transparent to the host and the executing application. This avoids premature declarations of faults, errors, or erasures and consequent host application aborts and other catastrophic measures. If the detected anomaly is not resolved within the allotted time, then other data recovery procedures can be invoked including device reset, the status reported to the host, and the next request processed.

Abstract: There is disclosed a method and means for increasing the positional accuracy of operator controlled cursors engaged in the digitized encoding of graphic information such as line drawings. The method steps comprise those of digitizing the instantaneous contact position between the cursor and the data entry surface as reference coordinates; detecting any segment of a colored object upon the surface within a predetermined area about the cursor; ascertaining the location within the area of the centroid or the like of the detected segment; and digitizing said ascertained location as a displacement from the reference coordinates. Apparatus for practicing the method comprises an independently actuable cursor formed from a position encoder and an image scanner, the scanner generating a Boolean coded array of points counterpart to a preselected surface area.

Abstract: An apparatus is disclosed for compressing a p .times. q image array of two-valued (black/white) sample points. The image array points are serially applied to the apparatus in consecutive raster scan lines. In response, the apparatus simultaneously forms two matrices respectively representing a high order p .times. q predictive error array and a p .times. q array of location events (such as the raster leading edges of all objects in the image). Improved compression is achieved by selecting between the more compression efficient of two methods for encoding the position of errors in the prediction error array. These alternative methods are conventional run-length coding and a novel form of reference encoding, used selectively but to significant advantage. Thus, a run-length compression codeword is formed from the count C of non-errors between consecutive errors (in response to the occurrence of each error in the jth bit position of the ith scan line of the predictive error array) upon either C.ltoreq.

Abstract: A method and apparatus for the point plotting and rearrangement of graphical data from a coded source into a buffer for raster type display. The execution of a graphic order in a stored program controllable graphics terminal are represented by a line generating a sequence of X Y coordinate values, which values are to be plotted or displayed. The points are plotted into a work organized memory array in the form of topologically adjacent rectangular subarrays. These subarrays are then transformed into linear arrays. In order to conserve memory they directly replace the previous topologically adjacent subarrays in the memory. The linear arrays may then be accessed a word at a time and applied to the raster display.