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.