The Code-Behind Page Model:

• HTML markup are kept in one file and the programming code in another file.

• There are two differences in the .aspx page between the single-file and the code-behind models:
• • In the code-behind model, there is no <script> block with the runat="server" attribute.
  • In the code-behind model, the @Page directive contains attributes that reference an external file and a class.

• The code file contains a partial class, which indicates that the class contains only some of the total code that makes up the full class for the page.  

• The partial class inherits from a base Page class (either System.Web.UI.Page or a class derived from System.Web.UI.Page). 

• The .aspx file contains an Inherits attribute that points to the code-behind partial class.

•  When the page is compiled, ASP.NET creates a new partial class for the .aspx file. This class is a peer of the code-behind partial class file and contains the declarations for the page’s controls.

• Finally, ASP.NET generates a class that inherits from the partial class created from the .aspx file and the code-behind partial class.

• The generated class is compiled into an assembly that runs in order to render output to the browser.