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Aucbvax.2060 fa.works utzoo!duke!decvax!ucbvax!cfh@CCA-UNIX Fri Jul 3 10:13:23 1981 Re: Question to field: Bit Mapped displays In response to your message of Thu Jul 2 20:26:38 1981:

Bit Map refers to the way a picture is stored, i.e. one bit (or aggregate of bits for color) of memory for each addressable point on the screen. As opposed to the older "display list" technique where the picture is stored as a list of line segments, etc.

Raster-scan refers to the method by which the picture is refreshed on the screen, in this case, as a series of horizontal lines, starting at the top of the screen and moving down. As opposed to "stroke writers" which move the beam in arbitrary directions to draw individual graphic primitives.

The earliest displays were stroke writers. The TX-0 at MIT moved a beam on a CRT under the direct control of the CPU. In some sense, this was the first personal computer, as refreshing the display didn't leave too many cycles for anything else. Later, the direct view storage tube (DVST) allowed the picture to be written just once instead of being refreshed 30 or more times per second. Only problem was that the only way to change anything on the screen was to erase the entire screen in a blinding flash which took .5 seconds. By the way, contrary to current publicity about the STAR, the Advanced Remote Display Station (ARDS) storage tube terminal was the first to offer the "mouse" as an input device.

Stroke writers are still in common use in the CAD/CAM area. They typically employ high-performance (expensive) analogue circuitry to draw vectors of much higher resolution than are currently feasible with raster displays. Resolutions of 4096x4096 are not uncommon.

The raster scanned bit map display is rapidly taking over the display scene. It is cheaper to build circuits which move the beam in nice sraight lines across the screen than to build in the ability to turn corners.

To answer your question, for all intents and purposes, raster-bitmap and bitmap mean the same thing.

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