What is the difference between DCS and PLC including date processing and architecture?

Difference is primarily in handling the analog control signals and control loops.
PLC is basically designed for logic (digital) signals which are mainly ON or OFF.
It has less capabilities in handling PID control loops with Analog signals.
On the other hand, DCS is basically designed to handle PID control loops with Analog signals.
Simply, if you have many control loops to be handled, it is preferably to choose the DCS otherwise is will be more economic to go to the PLC.
Both can do the job but it is a matter of pricing and complexity.

In PLC limited input and output used But DCS many more input and output used

This is a classic question while interviewing engineer candidate. It is all about term, marketing strategy and any other business matter. If you look back the history, originally we have relay system then so on... so on... and now Sie**** sounding PCS, Rock**** sounding PAS and even they say about programmable automation controller (PAC) rather than say PLC.

No matter what is the name, DCS, PLC, PAC, PCS, PAS and any others... i think the good company management and engineer will look at their requirements in detail first then find out the best    "automation system" match to their requirements. "The best" means money, continuous support, excellent service, etc.