With ASP.NET, you can separate user interface declarations from application logic.
Application logic is precompiled into DLLs that reside on the Web servers.
There are three groups of controls: HTML controls, ASP.NET controls, and SharePoint controls.
Controls are similar to Web Parts; you place them on a page and customize their properties to meet your needs.
ASP.NET Data controls allow you to define data sources and view the contents of data sources. The view controls must be bound to a data source.