Worker process recycling is the replacing of the instance of the application in memory. IIS 6.0 can automatically recycle worker processes by restarting the worker process, or worker processes, that are assigned to an application pool.
This helps keep problematic applications running smoothly, and minimizes problems such as memory leaks. You can trigger the recycling of the worker processes assigned to an application pool by using worker process recycling methods that are based on elapsed time, the number of Hypertext Transfer Protocol (HTTP) requests, a set time of day, and two kinds of memory consumption, in addition to recycling on demand.
To configure all the above settings, go to the Properties window of the application pool in which your Web application is running using the IIS manager. Using the Recycling, Performance, and Health tabs in the Properties window, you can specify values for the above settings.
IIS and ASP.NET: The Application Pool