Introduction
Generally, the concept of automatic control includes accomplishing two major operations; the transmission of signals (information flow) back and forth and the calculation of control actions (decision making). Carrying out these operations in real plant requires a set of hardware and instrumentation that serve as the platform for these tasks. Distributed control system (DCS) is the most modern control platform. It stands as the infrastructure not only for all advanced control strategies but also for the lowliest control system. The idea of control infrastructure is old. The next section discusses how the control platform progressed through time to follow the advancement in control algorithms and instrumentation technologies.