Why we go for the DCS inplace of PLC ?

DCS have much and more IO's than PLC and more accuracy .

DCS has advantages for process control system over PLCs.

DCS can handle Analog signal and can maintain there logs with the server redundancy. DCS is good for both  propotional control or for derivative control.

There was limitations in PLCs but now a days plcs improved and add such kind of  salient features as DCS have.