A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and communications protocol for communication. Input and output modules form component parts of the DCS. The processor receives information from input modules and sends information to output modules. The input modules receive information from input instruments in the process (or field) and transmit instructions to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexer or demultiplexers. Buses also connect the distributed controllers with the central controller and finally to theHuman–machine interface (HMI) or control consoles. See Process automation system.
The elements of a DCS may connect directly to physical equipment such as switches, pumps and valves or they may work through an intermediate system such as a SCADA system.