What is the Main disadvantage of layered approach to operating system design?

The main advantage of the layered approach is modularity. The layered are selected such that each uses function and services of only lower level layers. This approach simplifies debugging and system verification

In this case the system is easier to debug and modify, because changes affect only limited portions of the code, and programmer does not have to know the details of the other layers. Information is also kept only where it is needed and is accessible only in certain ways, so bugs affecting that data are limited to a specific module or layer.

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Praveen Muttikkal