A first computer workstation running windowed display system and applications programs produces a first video signal of a composite, windowed, display plus a first data signal indicating the dedications, positions, and sizes of all windows. A second computer asynchronously digitally communicates a second display signal to a communications controller and then to a display controller. The display controller also receives the first data signal plus the sync pulse of the first video signal. It produces, from the second display signal, a second video display signal that (i) is synchronized with the first video signal and (ii) contains display information positioned and scaled to be within a window dedicated to the second computer. It produces a switch control signal indicating the portions of each raster scan of the synchronized video signals that are inside and outside the dedicated window. The switch control signal gates in a video switch either the first or the second video signal to a video monitor. The video monitor displays windows showing information from the first computer plus a dedicated window showing information from the second computer.