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The IBM 2250 Graphics Display Unit was announced as part of System/360 in 1964. Unlike most modern computer displays, which show images in raster format, the IBM 2250 used vector graphics. A display list of line segments (vectors) on a 1024 by 1024 grid was stored in the computer's memory and repainted on the 2250's CRT up to 40 time per second. Characters were built of line segments specified by display list subroutines. Thus any character set or font could be displayed. The computer altered the display by changing the display list. As the display list got longer, the refresh time got longer too and eventually the display would start to flicker.
The 2250 was housed in a desk with an alphanumeric (QWERTY) keyboard and a separate programmed function keyboard which had keys, indicator lights and switches. A plastic overlay label could be placed over the function keyboard. Punches on the top edge of the overlay could be sensed by the computer so the keys, lights and switches could be reprogrammed simply by changing overlays. The 2250's CRT measured 21" diagonal, but the useful display area was 12 inch by 12 inch. A light pen was provided as a pointing device, serving the function of the modern computer mouse.
An IBM 2285 Display Copier could be attached to the 2250 to provide 8-1/2 by 11 inch hard copy of the display contents under operator control.
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