Postback forms in asp.net

It is a concept of html forms only when a form itself in its submission then we call this form/page as post back form/page. The basic question will be arise when we going thorough the postback concepts.How asp.net is related to this post back forms? If we create asp.net form we don't provide any action attribute to it. manually also it is not recommended to write action methods.
                               During rendering asp.net automatically writes action attribute which will call the some form or page name every asp.net form is a post back form. One more thing we have to know i:e why asp.net forces this post back concept.One of the main reason is to provide state management for page and its controls

 Note:- In asp.net 1.0/1.1 they was the only concept for post backs i:e straight post backs.Form asp.net 2.0 we can Even perform cross page post backs.Default is straight post back only