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Unformatted text preview: arious components of an operating system in the
sections above. We will now have a look at how these components are put
together to form an operating system.
Most modern operating systems organize their components into a number of layers
(levels), each built on top of lower layers. The bottom layer (layer 0) is the
hardware, and the highest layer (layer n) is the user interface. The number of inbetween layers and their contents vary from one operating system to another. How
this is decided is explained below.
The main advantage of the layered approach is modularity. The layers are selected
such that each layer uses the functions and services provided by its immediate
lower layer. This approach greatly simplifies the design and implementation of the
system because each layer is implemented using only those operations provided by
its immediate lower level layer.
Kernel The kernel of an operating system is its central controlling part that implements
the most primitive of the system's functions. It is the only part of an operating
system that a user cannot replace or modify. The precise interpretation of the
system's functions that are part of the kernel varies from one operating system to
another. However, typical operating system kernels contain basic functions that
are required for process management, memory management, device management,
and low-level security features like access control. In some systems, the kernel is
larger and provides for more than these functions, whereas in others, it is smaller.
Monolithic Kernel versus Microkernel
The two commonly used models for kernel design in operating systems are the
monolithic kernel and the microkernel. In the monolithic kernel model, most
operating system services such as process management, memory management,
device management, file management, and security are provided by the kernel. As
a result, the kernel has a large, monolithic structure.
On the other hand, in the microkernel model, the main goal is to keep the kernel as
small as possible. Therefore, in this model, the kernel is a very small nucleus of
software that provides...
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This document was uploaded on 04/07/2014.
- Spring '14