DISPLAY PROCESSOR MAPPING RAM.

In data processing a known technique is to use a mapping RAM (random-access memory) to keep a record of changes in a cache so that only changed data needs to be written back to bulk store. This article describes the application of this technique to a display processor where a frame buffer memory stores a direct mapping of a display screen. A block mapping RAM contains a single bit per N bytes of the memory automatically written by a main processor whenever a change is made to the display memory. The display processor continually scans the mapping RAM to detect changes in order to update the buffer memory. Alternatively, the display processor scans the mapping RAM only when a change has been made.