Integrated vs classic mode in IIS

What is application pool?
An application pool is a group of one or more URLs that are served by a worker process or a set of worker processes. Application pools set boundaries for the applications they contain, which means that any applications that are running outside a given application pool cannot affect the applications in the application pool.

Application pools offer the following benefits:
Improved server and application performance. You can assign resource-intensive applications to their own application pools so that the performance of other applications does not decrease.
Improved application availability. If an application in one application pool fails, applications in other application pools are not affected.
Improved security. By isolating applications, you reduce the chance that one application will access the resources of another application.

In IIS 7, application pools run in one of two modes: integrated mode and classic mode.

The Integrated Pipeline is one of the new features of Internet Information Services (IIS) version 7. It allows your HttpModules to participate in all requests, including those for static content, PHP pages and images.

The Classic Pipeline works just like IIS 6.0. All requests pass through the IIS pipeline first, and then if the file extension is mapped to ASP.NET ISAPI extension, then the request is handed to aspnet_isapi.dll and passes through the ASP.NET request pipeline. If the file is static file, ASP or PHP, it is handled by something else.

Most managed applications should run successfully in application pools with integrated mode, but you may have to run in classic mode for compatibility reasons. Test the applications that are running in integrated mode first to determine whether you really need classic mode.

Steps to change the application pool:

Click Start, then Run, then Type: inetmgr.exe , and click ok.
Once UI displayed, double-click the server name to expand it.
Click on Application Pools in the left pane.
Click the application pool you would like to change.
Now, click on “Basic Settings” on the right side.
A window will pop up that will give you access to change the Pipeline mode to either Classic or Integrated.