Operating Systems: Concurrent and Distributed Software Design

24.3. System structure and the UNIX kernel

UNIX provides a multi-user multi-programmed kernel-based operating system in which the kernel is responsible for accessing devices on behalf of applications, for scheduling access to resources and for enforcing protection between processes. This structure is illustrated in Figure 24.2 along with the major modules which comprise the kernel.

Figure 24.2. Outline of UNIX kernel modules.

In the figure, four example processes are shown as rounded rectangles. Two of these are system processes called init and the swapper; we will consider them in more detail in Section 24.6. The other two are ordinary processes ...