A general-purpose digital computer for the on-line control of large scale industrial processes serves the dual purposes of a time-shared controller for each loop by means of programmed algorithms and of a data logger and alarm scanner. The architecture of the general-purpose computer has been criticized regarding its suitability as a timeshared controller. This paper considers this problem and presents a case for the special-purpose digital controller. A research model is described in detail and its performance in a simulated system is given.