The Intel iAPX 432 is an object-based microcomputer which, together with its operating system iMAX, provides a multiprocessor computer system designed around the ideas of data abstraction. iMAX is implemented in Ada and provides, through its interface and facilities, an Ada view of the 432 system. Of paramount concern in this system is the uniformity of approach among the architecture, the operating system, and the language. Some interesting aspects of both the external and internal views of iMAX are discussed to illustrate this uniform approach.

This paper describes the fundamentals and some of the details of task communication in DEMOS, the operating system for the CRAY-1 computer being developed at the Los Alamos Scientific Laboratory. The communication mechanism is a message system with several novel features. Messages are sent from one task to another over links. Links are the primary protected objects in the system; they provide both message paths and optional data sharing between tasks. They can be used to represent other objects with capability-like access controls. Links point to the tasks that created them. A task that creates a link determines its contents and possibly restricts its use. A link may be passed from one task to another along with a message sent over some other link subject to the restrictions imposed by the creator of the link being passed. The link based message and data sharing system is an attractive alternative to the semaphore or monitor type of shared variable based operating system on machines with only very simple memory protection mechanisms or on machines connected together in a network.