Many people contributed to the contents of this document, which was thoroughly debated by electronic mail and debugged using two different prototype implementations for the Unix 4.3bsd operating system, one written by Louis Mamakos and Michael Petry of the University of Maryland and the other by Dennis Ferguson of the University of Toronto. Another implementation for the Fuzzball operating system [MIL88b] was written by the author. Many individuals to numerous to mention meticulously tested the several beta-test prototype versions and ruthlessly smoked out the bugs, both in the code and the specification. Especially useful were comments from Dennis Ferguson and Bill Sommerfeld, as well as discussions with Joe Comuzzi and others at Digital Equipment Corporation.