- A worker process runs as an executables file named W3wp.exe
A Worker Process is user mode code whose role is to process requests, such as processing requests to return a static page.
The worker process is controlled by the www service.
worker processes also run application code, Such as ASP .NET applications and XML web Services.
When Application pool receive the request, it simply pass the request to worker process (w3wp.exe) . The worker process“w3wp.exe” looks up the URL of the request in order to load the correct ISAPI extension. ISAPI extensions are the IIS way to handle requests for different resources. Once ASP.NET is installed, it installs its own ISAPI extension (aspnet_isapi.dll)and adds the mapping into IIS.
When Worker process loads the aspnet_isapi.dll, it start an HTTPRuntime, which is the entry point of an application. HTTPRuntime is a class which calls the ProcessRequest method to start Processing.
For more detail refer URL
http://aspnetnova.blogspot.in/2011/12/how-iis-process-for-aspnet-requests.html