Thanks to the page model introduced in ASP.NET 1.x, the compilation process for an ASP.NET Web page has always been divided into two phases. First, the code-behind files and any other supporting classes are compiled into an assembly, and then the individual ASPX files are compiled at runtime. Although this model has many advantages, it has a few drawbacks. ASP.NET 2.0 offers several alternatives to the basic model, providing a wider range of compilation options depending on your specific needs.

Compilation in ASP.NET 1.x:

The primary compilation model in ASP.NET 1.x resulted in one application assembly (containing all of the compiled code-behind files and other source code) and one temporary assembly created for each ASPX page that was requested. In some cases, compiler optimizations such as batching may cause the temporary ASPX pages to be compiled into the same assembly. In either case, each ASPX page is compiled into a temporary assembly so that it can be loaded into the ASP.NET runtime.