4.) SYSTEM STRUCTURE

Simple Structure

>View the OS as a series of levels
>Each level performs a related subset of functions
>Each level relies on the next lower level to perform more primitive functions
>This decomposes a problem into a number of more manageable subproblems

Layered Approach

The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.