Hi Team,
 My name is balaji and i am new to salesforce development. And i am having one doubt on controllers excution.

In which mode standard controller will work, either in user mode or system mode?
In which mode custom controller will work, either in user mode or system mode?
In which mode extensions with custom controller  will work, either in user mode or system mode?
In which mode extensions with standard controller  will work, either in user mode or system mode?

Thanks in advance.

Regards,
Balaji.A
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Hi team,
My name is balaji. I am new to salesforce development. I have one doubt.

why we having custom controllers, we can also achieve the things by using standard controller with extension controller.

Thanks in advance.