Principles of Object - Oriented Operating System Design

This paper presents three principles for the design and construction of objectoriented operating systems. These principles are based on the design of Choices, an object-oriented operating system that is implemented on the Encore Multimax shared memory multiprocessor. Choices is written entirely in C++, an object-oriented language that supports inheritance through class hierarchies. C++ is compiled, rather than interpreted, so Choices executes directly on the hardware without any special run-time support. The rst principle is to model the hardware/system software interface by a framework of interacting components. The state of the model should re ect the state of the hardware and manipulation of the model should modify the state of the hardware. The second principle is to provide a uniform mechanism for application-to-system and for application-to-application communications. In an object-oriented operating system architecture this should be the invocation of a method on an instance of a system or application object. The third principle is to organize an object-oriented operating system as a member of a family of operating systems. This family should be represented as a class hierarchy that forms a taxonomy for operating system algorithms and data structures. We discuss these principles using examples taken from the Choices family of operating systems.