This research investigates the capability of a multiprocessor system in guaranteeing the execution of critical tasks and determines the cause of deadline failures. By implementing a real-time application using an INMOS transputer and Occam language, we were able to distribute required tasks among the processors and determine their CPUs usage. We evaluated the performance of the system in terms of the number of guaranteed critical and non-critical tasks, arrival rates, and conflicting deadlines.

An overview is provided of each of the alternate computer networking standards, specifically the IEEE 802 protocols and fiber distributed data interface (FDDI), which can be used effectively in real-time distributed systems. An analysis is given to provide a comparison of their relative strengths and weaknesses in supporting real-time distributed systems. A model is developed to provide the means to investigate the performance of each individual standard in terms of the number of messages that are transmitted successfully and the number of messages that cannot be transmitted prior to their deadlines. Fine tuning of the network parameters is discussed as well as the conditions under which each individual standard operates most efficiently.>

Described are the major features of the completely decentralized adaptive file system Melody, which runs on top of the distributed operating system Dragon Slayer. A definition of all major design requirements is presented, along with a heuristic algorithm for resource scheduling which allows for replicating, relocating, or deleting file copies in a local area network. At every site a local task scheduler tries to schedule the arriving critical tasks such that no deadlines are missed, based on the availability of resources at this site. Depending on the task-deadline failure history and file-access request history at each node, file copies may be relocated, replicated to other sites, or deleted. Such copies may also assume a different status (public or private) depending on how recent their information is. Only public copies are maintained under a strong concurrency-control protocol. The idea is to maintain optimal distribution of file copies in the network regarding reliability and real-time responsiveness of the system. Experiments performed to analyze Melody's capability of minimizing deadline failures of time-critical tasks were compared to structurally simpler file-system models. A report is presented on the distributed simulation results which show Melody's superior performance and its built-in sensitivity to changes in the environment.>

The authors analyze current and future needs in building adaptive real-time systems and formulate a series of design requirements for their hardware/interconnection, operating system, and application levels that could be satisfied together only in an integrated system design. They describe the major features of the corresponding model. On the operating-system level, novel services are rendered by their own file system, Dragon Slayer. The file system, in order to both meet real-time constraints and provide for high availability in a hazardous environment, allows for replicating, relocating, or deleting of file copies. A distributed implementation of the integrated system design model is currently being completed in order to serve as a distributed real-time testbed. The authors also report on a sensitivity study that shows how promptly the model file system reacts to changing environmental situations (changing request patterns).>