What are the differences between DCS and PLC/SCADA systems?

DCS differences from PLC/SCADA: Integration - DCS provides fully integrated control, HMI, historian, and asset management from single vendor; scalability - DCS designed for large continuous processes (thousands of I/O); control strategy - DCS emphasizes continuous/analog control, PLCs emphasize discrete/sequential; database - single integrated database in DCS vs separate databases in PLC/SCADA; redundancy - built-in controller and network redundancy in DCS; and cost - DCS has higher initial cost, lower lifecycle cost for large systems. PLCs with SCADA are preferred for smaller systems, discrete manufacturing, and where flexibility in component selection is desired.