简单说SCADA跟DCS的区别类似于 RTU跟PLC的区别。
SCADA:
1. is event drivent, a SCADA system in process events，一个状态的改变系统会产生报警、数据更新、相应的处理
2. 主要是考虑状态的改变，包括状态点，模拟量的改变，
DCS:
1. is process state driven, primarily interested inprocess trends.
2. DCS software tasks are generally run sequentially, rather than event driven. Therefore alarms or events are not generated when a point changes state, but when that particular process is run.
3. DCS系统一般是直接跟I/O打交道，即硬接点。
These underlying differences prompt a series of design decisions that require a great deal more complexity in a SCADA system database and data-gathering system than is usually found in DCS. DCS systems typically have correspondingly more complexity in their process-control functionality.
Modbus是DCS的一种协议，报告每次被扫描的数据点状态，不报告两次扫描之间的变化，是属于报告“当前状态"的一种系统。
IEC 60870-5-101 变电站的一种SCADA procotol。报告被监控点的变化和这些变化的时标，而且有优先级，能优先报告数据。