Patent US 4,785,296

A display system which uses one display unit as if it were a plurality of display units to separately display whole information and partial information of document is disclosed. A plurality of display windows are defined on one display screen and a layout or a reduced image of the whole information is displayed in one of the window and information or image representing the information of a partial area of the whole information is displayed in other window. When one of the whole information and the partial area information is changed, the other information is also changed correspondingly, or a mark indicating a relation between the whole information and the partial area information is displayed in one of the window.