Usually, ‘process control’ refers to a closed feedback system in which an industrial process (like making chocolate bars or paint) is regulated by constantly monitoring the output of the process and feeding back a part of this signal to regulate a production variable (say, the amount food coloring in the chocolate bars) to within a specific limit.
Instead of controlling how many corn flakes to put in a box of cereal however, the biggest ‘process control’ customer for the PDP-1 was International Telephone & Telegraph (ITT), at the time one of the largest long distance communications carriers in the world. The ITT application was based on PDP-1s slightly modified to handle message switching, in the process revolutionizing the way ITT handled its Teletype traffic. ITT purchased 19 PDP-1s, making it DEC’s biggest customer.
Gordon Bell observes that the ITT order allowed DEC to build manufacturing momentum by not having to make every machine a custom order: “If that hadn’t happened, I don’t think we would have survived in the computer business.