Difference between 'classic' and 'integrated' pipeline mode in IIS7

Classic mode (the only mode in IIS6 and below) is a mode where IIS only works with ISAPI extensions and ISAPI filters directly. In fact, in this mode, ASP.NET is just an ISAPI extension (aspnet_isapi.dll) and an ISAPI filter (aspnet_filter.dll). IIS just treats ASP.NET as an external plugin implemented in ISAPI and works with it like a black box (and only when it's needs to give out the request to ASP.NET). In this mode, ASP.NET is not much different from PHP or other technologies for IIS.

Integrated mode, on the other hand, is a new mode in IIS7 where IIS pipeline is tightly integrated (i.e. is just the same) as ASP.NET request pipeline. ASP.NET can see every request it wants to and manipulate things along the way. ASP.NET is no longer treated as an external plugin. It's completely blended and integrated in IIS. In this mode, ASP.NET HttpModules basically have nearly as much power as an ISAPI filter would have had and ASP.NET HttpHandlers can have nearly equivalent capability as an ISAPI extension could have. In this mode, ASP.NET is basically a part of IIS.



Difference--2

Classic mode is where IIS only works with ISAPI extensions and ISAPI filters directly. This is how IIS 6 and below behaved. Using classic mode, ASP.NET is simply an ISAPI extension (aspnet_isapi.dll) and an ISAPI filter (aspnet_filter.dll). When using classic mode the server uses two piplines to handle requests, one for native code and the other for managed code. In this mode the application doesn't take full advantage of everything IIS 7.X has to offer.
Integrated mode handles all requests through a unified pipeline for IIS and is tightly integrated with ASP.NET through that same pipeline. ASP.NET sees every relevant request and manipulates things along the way rather than acting as an external plugin. With integrated mode ASP.NET runs much more efficiently in IIS and will yield greater performance for your site.