What is the difference between SCADA & DCS ?

1. DCS is process oriented while SCADA is data oriented.

2. DCS concentrates on control process and present data to user/ operator while SCADA concentrates on demands of control system.

3. SCADA maintains a database while DCS is always connected to its data source and no need of database.

4. DCS has a closed-loop control system at PCS/RTU level while SCADA does not have it.

* Most DCS and SCADA systems today come with same standard facilities like events, archiving, HMI, reporting, DB management and logging as well as remote control centers. 

for detail study:

http://control.com/thread/1365080091

An automation system within a campus is usually refferred to as a DCS, while SCADA systems comprise of different stations disributed over large geographical areas.

DCS can be deployed for the supervision of a cretain process, however if a number of DCS systems at different locations are interconned to a master station, they form a SCADA system.

to cut a long answer short ,DCS is more of a controller while SCADA is more of a supervisory monitoring system with some control functions