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Graphics can be implemented as a virtual system resource. This abstraction appears to each application on a multiprocessing workstation as a dedicated rendering and display pipeline. A variety of simple mechanisms support the simultaneous display of different types of images and eliminate the need for low-level device driver software. They permit applications to embed graphics instructions directly in their code. The abstraction allows for cleaner software design, higher performance, and effective concurrent use of the display by several applications.
Voorhies et al. (1988) studied this question.