When use DSC system, when PLC system!

Until now, I have been used PLC from Siemens, Omron and AB. They run very OK, They integrated many( alanog, digital signal, special function module). about DSC, when we use DCS. I understand DCS is design for dedicated purpose, software, field hardware, control hardware of same company?. Am I wrong?.
Thank you!

In general I would recommend using PLCs on any new system, and using DCS only when adding to existing systems. DCS is usually proprietary and more expensive.

The two technologies are blending. New DCS equipment looks alot like PLCs, and new PLCs have many of the communications features and analog control features that originally could only be found in a DCS.

DCS developed because plants that automated process control early had a lot of independent PID controllers that they wanted to tie together in a single communciations and display network. PLCs in the early days were essentially applied to discrete componnent manufacturing like automotive plants, and each machine was independent.

Thank Tom Jenkins!