Abstract: A display device which has a zooming function and is required to display a logical screen larger in size than a physical screen, is operated in the following manner. When an action for indicating a zooming command is taken, a first rectangular frame similar in shape to the logical screen, a second rectangular frame similar in shape to a logical area which is now displayed on the physical screen, and a third rectangular frame similar in shape to a logical area which is to be subjected to a zooming operation, are all displayed on the physical screen, and moreover the third rectangular frame can be moved to a desired position by means of a coordinate input device such as a mouse. Hence, the zooming operation and a desired logical area corresponding to the third rectangular frame placed at the desired position can be specified by a one-touch operation. Thus, the operation procedure becomes simple, and the operability of the display device is improved.

Abstract: In a multiwindow system in which a plurality of windows are set on a display screen at positions such that these windows partially overlap and the display priority and position of each window can be arbitrarily changed, when the operator instructs to change the display priority of the window, a check is automatically made to see if there exists the window which will be completely covered by the other windows having priorities higher than that of this window and will fully disappear from the screen if the display priority is changed or not. If such a window is found out, the display priority of this window is changed in the state in which this window is automatically shifted to the position where a part of this window can be seen on the screen, thereafter the window is displayed on the screen.