This paper describes an architecture that provides support for quality of service (QoS) in open systems. The Quartz QoS architecture aims to avoid the dependency on specific platforms that limits the application of most existing QoS architectures in open, heterogeneous and distributed systems. Quartz adopts a flexible and extensible platform-independent design that allows its internal components to be rearranged dynamically, adapting the architecture to the surrounding environment in order to accommodate the differences among diverse computing platforms. Further significant problems found in other QoS architectures, such as the lack of transparency, flexibility and expressiveness in the specification of QoS requirements and limited support for resource adaptation, are also addressed by Quartz. This paper compares Quartz to other QoS architectures found in the literature, presents a prototype implementation of Quartz, and shows how Quartz is integrated with CORBA to form a framework for control and transfer of streaming media.