What is a layered approach and what is its advantage?

Layered approach is a step towards modularizing of the system, in which the operating system is broken up into a number of layers (or levels), each built on top of lower layer. The bottom layer is the hard ware and the top most is the user interface.The main advantage of the layered approach is modularity. The layers are selected such that each uses the functions (operations) and services of only lower layer. This approach simplifies the debugging and system verification.