The most fundamental change in IIS is the way it now processes requests from clients. In previous versions of IIS, a user-mode application was responsible for accepting requests and then sending them on to a separate application to be processed. This mode of operation severely limited both the performance of IIS and its stability because an external application could easily slow down or completely crash the IIS service. IIS 6 gets around this by moving the responsibility of accepting requests to the kernel and then providing protected memory spaces for individual Web applications.