System calls and interrupt vectors in an operating systems course

The introductory operating systems course has a tendency to appear to the student as a disparate collection of topics such as synchronization primitives, process scheduling algorithms, and page replacement policies. We describe a sequence of material to cover early in the operating systems course that prevents this tendency by clarifying the goal of the course and by providing a framework for understanding how the later course material is used in kernel design. The material centers around two concepts. First is the importance of the abstraction provided by the system call interface, that the kernel is the implementation of that interface, and the analogy with the instruction set interface the student has already encountered. Second is how the interrupt vector mechanism in a broad sense is central to how the kernel functions and underpins the actual implementation of many of the other topics in the course. Illustration through code from a real operating system kernel is a key feature of how this sequence makes clear the workings of an operating system.