Difference between .NET Extensibility and ASP.NET

In versions of IIS prior to 7.0, the ASP.NET pipeline was separate from the web server's request processing pipeline. The web server's functionality was usually extended via ISAPI filters and extensions.

However, in IIS 7.x they are more tightly integrated, which allows for the server to be extended using managed code, via the ASP.NET extensibility APIs. Two primary ways this can be done are via modules and handlers, which are quite similar to ISAPI filters and extensions respectively.

The APIs of interests are:

• System.Web.IHttpModule
• System.Web.IHttpHandler
• System.Web.IHttpAsyncHandler.

You can read more about how to extend the server in the articles below.

http://learn.iis.net/page.aspx/243/aspnet-integration-with-iis-7/

http://learn.iis.net/page.aspx/170/developing-a-module-using-net/

http://msdn.microsoft.com/en-us/magazine/cc164128.aspx#S4

This site talks about .Net extensibility in relation to IronPython: http://www.asp.net/learn/whitepapers/ironpython

You might want to review more info at this site: http://aspnetextensibility.com/

Assuming your developing asp.net sites in c# or vb.net then you will need the ASP.Net support. To sum up, it's probably one of those things you'll be able to define when you actually need the .Net Extensibility option installed.

However, if you really want to know: .Net Extensibility is an IIS 7 feature which brings the ability to extend IIS 7 via the runtime extensibility model into the core server product.

Building "regular" sites (whatever those are), don't worry about it. Needing to get down and dirty by modifying the pipeline through modules or handlers? Install it. Either way, you are still going to need the regular ASP.Net support installed.

With regards to what the MS guy said about the Hello World file.. Ignore that, he didn't read the full question...