The IBM 2250 Graphics Display Unit was announced with System/360 in 1964. A complete 2250 III system with controller cost around $280,000 in 1970, though up to 4 displays could share a single controller, reducing the cost per display by up to 40%. A display list of line segments on a 1024 by 1024 grid was stored in computer's memory or an optional buffer on the 2250 and repainted on the 2250's CRT up to 40 times per second. The computer altered the display by changing the display list. 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. An optional character-generator feature on all models provided predefined fonts of 63 characters to simplify display of alphanumeric information. The 2250 was housed in a desk with an alphanumeric 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 2250s 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 8½ by 11 inch hard copy of the display contents under operator control. An IBM 2280 Film Recorder or IBM 2282 Film Recorder/Scanner could be attached to a 2840 control unit providing for output or input/output to photographic negative. There were four models of 2250:
Model 1 – attached directly to a System/360 via a selector or multiplexor channel.
Model 2 – attached via a 2840-1 control unit. A 2840 could attach up to four 2250s and provided buffering and a character generator.
Model 4 – attached to an IBM 1130 minicomputer via the storage access channel. The 1130 could run either as a standalone processor or as a front-end processor connected to a remote System/360.
