IBM 2250 Graphics Display Unit

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 2250s 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, although fonts were generally extremely simplified for performance reasons. 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.