A QOS control is one of the most important factors in continuous media applications. The QOS levels of the applications should be maintained even if several continuous media applications are running concurrently. Also, the QOS levels should be changed according to a number of applications and their respective importances when a system is overloaded. This paper presents our experience with a video-on-demand system that supports a dynamic QOS control scheme on Real-Time Mach, and shows the necessity of a real-time resource management for building such applications.