title: Difference between ISAPI filter and ASP .NET Http module
body: <p>Being as ASP .NET developer, today I was exploring internal working of IIS web server when this <code>ISAPI filter</code> hit me. I have an idea of ASP .NET web request inside ASP .NET run time where we have two concepts:</p>
  
  <ol>
  <li><code>HTTP Modules</code> : Acts as request filer before your request hits an HTTP handler. You can analyse http headers at this stage to take conditional decisions.</li>
  <li><code>HTTP Handler</code> : The end point of any http web request which does the actual processing of your *.aspx page request.</li>
  </ol>
  
  <p>So I got confused between <code>HTTP Modules</code> and the <code>ISAPI modules</code> exposed by an Internet web server like IIS. Can someone help me understand the difference between the two? Also do they have any roots in the CGI web request serving paradigm from older era of web servers?</p>