Question

Hi there,

Thanks for your quick response in Advance .

Best,

- Operating systems typically split functionality into layers.

- Explain what it means and how it works

- Explain the advantages and disadvantages of the structure of software as layers in distributed systems.

Thanks a Lot!!

Answer 1

Operating system can be made in modular using many ways. One method from them is layered approach.

In this approach, OS can be broken up into different number of levela or layers. The highest layer(layer N) is UI(user interface) ad bottom layer means layer 0 is the hardware. Design of these layers are done in such a way that each layer uses the functions of the lower layers only means layers can only interect with the layers that are below it. For debugging process, it always starts with lower layer. It helps into debugging that if any error occurs in a particular layer then we can say that the error is in that layer because it's all lower layers are already debugged.

So, main advantage of this approach is can be constructed simply and debugging. But the difficulty is to define the different layers.

Different layers in this approach from lower to higher are hardware, CPU schedulling, memory management, process management, I/O buffer, User programs etc..

For example, MS windows NT in which the lowest layer is a monolithic kernel and many components presents at higher level.

Advantages of layered approach in distributed system :

• Simply constructed
• Easy for debugging
• increases flexibility, maintainability and scalability because in layered approach, UI is separate from business logic and business logic is separated from data access logic.
• Multple app can use the components

Disadvantages of layered approach in distributed system :

• negative impact on performance because we have extra overhead when passing through all the layers. for example if user executes an i\o operation, it need to execute a memory management layer, which in turn calls to CPU scheduling layer, which in turn calls to hardware. At each layer, parameters can be modified.
• Hard to define each layer in the distributed system.