Application pool

Prior to IIS 6.0 all the webapplications  used to run at the same place in iis server.

When one webapplication get affected  that in turn used to effect all the webapplications running in the server.

So in IIS 6.0 a new concept  called Application Pool came in to picture.

Application pools provide a isolation between the webapplications so that when one worker process or application is having an issue or recycles, other applications or worker processes are not affected.

So in this way Apllication pools provide more security and reliability  with the concept of isolation.