Video display mode for dual displays

A controller, for two display units of a computer system, includes two control elements, VC 1 and VC 2 , having separate connections to the display units. In a dual image (DI) mode of operation, VC 1 and VC 2 process different data to produce different images at respective display units. In a single Image (SI) mode, VC 1 and VC 2 process the same data to produce identical images. In DI mode, data applied to each control element represents a portion, less than the whole, of a virtual desktop scene having a display width exceeding width resolution settings of respective displays. In this mode VC 1 can be controlled manually to scan the entire virtual scene piecemeal, while VC 2 is constrained to process only a fixed portion of that scene. In a preferred embodiment, the virtual scene includes private and public areas. The private area shows notes intended for viewing only by a presenter of images shown in the public area, and the public area shows images viewable both by the presenter and an audience. In this arrangement, the display connected to VC 1 can display the entire virtual scene to the presenter in a piecemeal fashion, while the second display shows only the public area to the audience.