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A distributed computer system (DCS) is a collection of computers connected by a communications subnet and logically integrated in varying degrees by a distributed operating system and/or distributed database system. Each computer node may be a uniprocessor, or multiprocessor, or a multicomputer. The communication subnet may be a widely geographically dispersed collection of communication processors or a local area network. Typical applications that use distributed computing include e-mail, teleconferencing, electronic funds transfers, multi-media telecommunications, command and control systems, and support for general purpose computing in industrial and academic settings. The wide spread use of distributed computer systems is due to the price-performance revolution in microelectronics, the development of cost effective and efficient communication subnets [4] (which is itself due to the merging of data communications and computer communications), the development of resource sharing software, and the increased user demands for communication, economical sharing of resources, and productivity. A DCS potentially provides significant advantages, including good performance, good reliability, good resource sharing, and extensibility [35,41]. Potential performance enhancements is due to multiprocessors and an efficient subnet, as well as avoiding contention and bottlenecks that exist in uniprocessors and multiprocessors. Potential reliability improvements are due to the data and control redundancy possible, the geographicaldistribution of the system, and the ability for hosts and communication processors to perform mutual inspection. With the proper subnet, distributed operating system [46], and the distributed database [85], it is possible to share hardware and software resources in a cost effective manner, increasing productivity and lowering costs. Possibly the most important potential advantage of DCS is extensibility. Extensibility is the ability to easily adapt both short and long term changes without significant disruption of the system. Short term changes include varying workloads and host or subnet failures or additions. Long term changes are associated with major modifications to the requirements or the content of the system. DCS research encompasses many areas, including: local and wide area networks, distributed operating systems,distributed databases, distributed fileservers, concurrent and distributed programming languages, specification languages for concurrent system, theory of parallel algorithms, theory of distributed computing, parallel architectures and interconnection structures, fault detection and ultrareliable systems, distributed and real-time systems,cooperative problem solving techniques of artificial intelligence, distributed debugging, distributed simulation, distributed applications, and the methodology for the design, construction and maintenance of large, complex distributed systems. Many prototype distributed computer syst