Abstract: A simulator for a distributed process control system utilizes a simulator station as an interface between a plant modeling computer and an instrumentation and control system which uses actual distributed processing units (DPUs) running actual process control software. The simulator station memory maps sensor signals received from the plant modeling computer through reflective memory directly to a memory-mapped input/output (I/O) interface of each DPU at the scan rate, or a multiple of the scan rate, of the DPU, and provides the control signals generated by the DPUs to the plant modeling computer at the same rates. A data highway such as in the actual system provides communications between the DPUs and between the DPUs and operator stations, (and potentially other man-machine interface stations) which provide operator signals used by the DPUs.