An application pool is a worker process to which you can assign Web applications. By using application pools to isolate Web applications, you can improve application security by reducing one application’s ability to access another application's resources. This separation also helps to prevent the Web applications in one application pool from negatively affecting the availability of Web applications in another on the same Web server. For example, if one Web application fails or consumes excessive resources, in the majority of cases, applications in other application pools on the Web server are not affected.
Creating too many application pools on a Web server may adversely affect Web server performance.
Create an application pool.
Add a Web application to an application pool.