Use the Add Application Pool and Edit Application Pool dialog boxes to create or edit an 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 that they contain; these boundaries prevent applications in one application pool from affecting applications in another application pool.
UI Element List
Type a unique, friendly name for your application pool. You can use this name to easily identify the application pool later, and to simplify the assignment of applications to the application pool.
.NET Framework version
Select the version of the .NET Framework that will be loaded by this application pool. If the applications that you want to assign to this application pool do not contain managed code, select the No Managed Code option from the list.
An application pool can load only one version of the .NET Framework; all applications in the application pool must use the same version.
Managed pipeline mode
Select one of the following values from the list to specify how IIS processes requests for managed content:
Start application pool immediately
Select this option to enable the application pool to start whenever the Windows Process Activation Service (WAS) is started. If you disable automatic startup, you must start the application pool manually or else requests made to applications in the application pool will return an HTTP 503-Service Unavailable error.