The evolution of a graphics system for linked computers

The development of a comprehensive two‐dimensional graphics package for an ICL 4130 with a high‐speed data link to a DEC PDP‐7 with Type 340 refreshed C.R.T. display and light pen is traced from its origin as a package of ALGOL procedures for graphical output. The design criteria imposed by the requirements for light‐pen tracking and identification of picture parts are described, and decisions which affected the subsequent development of the sysetm are identified and commented upon. The various types of display file editing which may be performed are described, and a facility mentioned for saving display files on the backing store of the PDP‐7. The idea of a ‘fixed‐function satellite’ is introduced and its potential usefulness in other operating environments discussed.