Abstract: A system for selectively controlling individual expansion slots in an IBM-AT/NEC 9801 dual compatible computer provides automatic control for the individual ISA bus expansion slots in the computer. This facilitates the use of an Industry Standard Architecture (ISA) bus and ISA (AT) type add-on cards in the dual compatible computer. A user configures each slot as containing either a card which may interfere with operations of the computer in the non-IBM-AT compatible mode or a card which will not interfere with computer operations in the non-IBM-AT compatible mode. Thereafter, the computer automatically disables the cards in accordance with the mode of computer operation.

Abstract: Color dither patterns are read into a pixel bit map memory used to form a color display by means of concurrently addressing a pattern memory storing the dither patterns. Lower order address bits repeatedly access a preselected portion of the pattern memory to supply the dither pattern which is written as data into the pixel bit map memory.

Abstract: Graphics commands for a display are listed and divided into sublists corresponding to separate strips or bands of the display, and these sublists drive the display memory consecutively and substantially concurrently with the processing of additional sublists. Graphics commands relating to graphics extending between bands are transferred to successive sublists during processing to provide their display in successive bands. A pair of band size bit map memories are alternately loaded with band information and read out.