Abstract: Display data is stored in a display memory in densely packed format in all display modes under control of memory controller logic which modifies original addresses for mapping display data into the display memory such that a stream of data for driving a display device can be generated from sequential memory locations. This enables the display memory to take advantage of the benefits of dual-ported memory technology whilst maintaining compatibility with VGA display modes. In order to provide complete VGA compatibility, even in unusual applications, a duplicate auxiliary display memory for the storage of the display data in accordance with the original addresses can be provided. This auxiliary display memory is not used for updating the display, but solely for the retrieval of the display data.

Abstract: A display system has, in addition to a display memory for the main storage of display information for a character mode, a separate cache for the temporary storage of the definitions of one or more fonts currently required for display and control logic for updating the font cache from the display memory. This enables the efficient support of a character mode on a display system, particularly where the display memory of that system is implemented with dual-ported memory technology. Compatibility with existing display standards is achieved.

Abstract: In a display system having a palette for chrominance and/or luminance information, a display buffer for information defining the pixels of a display field, including index values for indexing the palette select the chrominance and/or luminance of the pixels, a windowing mechanism is provided for associating a different range of index values with each of a plurality of windows and for responding to index values stored at individual pixel positions in the display buffer to determine the visible extent of a given window within the display field. This allows a plurality of windows to be displayed with a minimum of extra logic and without unduly constraining the choice of colors available within those windows. In the described embodiment, windows are defined in a first phase by storing index values from the range of values associated with that window at all pixel positions for that window.