We have studied in detail the organization of Xinu. Naturally, this organization is far from the only one used in current operating systems. In many respects it is the simplest of the ones adopted. In this discussion we first look at the main characteristics of the Xinu organization and then study variations of it that are supported in other operating systems.
The organization of an OS identifies the various boundaries between its components and the boundaries between these components and user programs. These boundaries can be logical, that is, visible to the programmer or physical, that is, transparent to the programmer. A module scope is an example of a logical boundary whereas an address space or memory page is an example of a physical boundary.