What is difference between SCADA and DCS?

SCADA is an abbreviation for Supervisory Control and Data Acquisition .

DCS stands for Distributed Control System.

Normally, a SCADA system will get the data from a RTU (remote terminal unit). A RTU runs independently, except for some control from the central supervisory system such as fire fighting, emergency shut-down (i.e water & oil pipelines). The communication path will be through a GSM, wireless technology, etc...

For a DCS system, it controls the process as a stand-alone system. It has the control loops built into it's own controller. The communication path will be through something like a LAN high-speed Ethernet, or other communications network. DCS is a single unit, or a group of local units

I think that my clarification helps a little bit on the subjects of DCS and SCADA.