The growth and popularity of loosely-coupled distributed systems such as the World Wide Web and the touting of Java-based systems as the solution to the issues of software maintenance, flexibility, and security are changing the research emphasis away from traditional single node operating system issues. Apparently, the view is that traditional OS issues are either solved problems or minor problems. By contrast, we believe that building such vast distributed systems upon the fragile

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... e provided by today's operating systems is analogous to building castles on sand. In this paper we outline the supporting arguments for these views and describe an OS design that supports secure encapsulation of the foreign processes that will be increasingly prevalent in tomorrow's distributed systems. 1