Introducing ASP.NET MVC 4
When Microsoft first introduced ASP.NET in 2002, it had a single programming model called Web Forms that allowed developers to quickly build web applications in a way that was familiar (to those who built applications with Visual Studio) and intuitive. At the time, the Web Forms model was a breakthrough. Although in many ways the model was a black box, it definitely moved the state of web development forward.
In Web Forms, web pages are (normally) represented by two files, one with extension .aspx that defines the user interface, and another with extension aspx.cs or aspx.vb (depending on the server language, ...