What are the various differentiate between a custom controller and the controller extensions in Salesforce?

There are some similarities and differences between two controllers. Let us see how they resemble each other and in what aspect are they different?

1. Both allow custom objects, custom data sets, and the custom actions. They help in leveraging existing data and actions within a standard controller.

2.The Custom controller should contain all data and actions within a page that will be executed later. At the same time, controller extensions allow data or auctioned that is extended in the form of buttons, links, custom overrides etc.