System Structure

Simple Structure

– any part of the system may use the functionality of the rest of
the system
– MS-DOS (user programs can call low level I/O routines)

Layered Approach

– layer n can only see the functionality that layer n-1 exports
– provides good abstraction from the lower level details
• new hardware can be added if it provides the interface required of a particular layer
– system call interface is an example of layering
– can be slow if there are too many layers