In this paper, the authors propose a multiwindow system that can smoothly execute window operations such as moving, resizing, or scrolling by using a combination of a drawing-time composition method and display-time composition method. Memory for storing the image of the window for which the window operation is to be performed (operation target window) and memory for storing a composite image of all other windows generated by a drawing-time composition method are both established in this system. The image that is displayed on the actual screen is obtained by using a display-time composition method to combine images that were read in parallel from both of these memories to generate the multiwindow image. The authors performed a trial experiment using a 640-pixel by 480-pixel display device to verify that no flicker appeared on the display screen when updating the operation target window. From the results of this trial experiment, they suggested that smooth window operations probably can also be executed for a 1280-pixel by 1024-pixel display device. (C) 2004 Wiley Periodicals, Inc.