ISAPI vs httphandler

In IIS6 was there a reason for using ISAPI filters/ extensions?. Can the same not be achieved using httphandler/ http modules. Also in IIS7 has ISAPI been removed completely ?. Is the entire code of IIS7 written i开发者_开发技巧n .Net. I want to know should one know about ISAPI in detail for debugging or adding new features ?

In IIS6, ISAPI filters / extensions were analogous to HttpModules / HttpHandlers. In terms of HttpModules, they cannot deliver the exact same functionality as ISAPI filters. One limitation is that non ASP.NET resources do not have access to the HttpModules. For example, if your application is classic ASP and you wanted to manipulate the incoming requests and outgoing responses then your only option would be an ISAPI filter.

IIS7 still supports adding ISAPI filters and extensions.

In general, ISAPIs time has come and gone. If you are looking to extend web server functionality with IIS7 then the .NET modules and handlers interfaces are the best approach.