The TELETYPE+ 5620 DMD is a highresolution bitmapped display terminal.The 5620 screen may be divided into a number of rectangular windows,called layers,each of which appears to a UNIX* System host as a separate terminal.A multiplexing communications protocol allows each layer a private full-duplex communications channel to the host.Layers may arbitrarily overlap,yet all are concurrently updated.Graphics operations in a layer are automatically performed in the visible portion and in all affected obscured portions of the layer.The result is that changes are immediately visible and the obscured portions are always up-todate.This paper briefly describes the layer concept,discusses the implementation of 5620 software on UNIX System Ⅴ and shows some examples of the usefulness of the 5620.
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