Operating Systems Structures

Operating Systems Structures

• There are various ways used to structure OS’s
• Simple Structure – MS-DOS
• Complex Structure – UNIX
• Layered Structure
• MicroKernel Structure

Layered Approach

• One way to make the OS modular
• The OS is divided into a number of layers (levels)
• Each layer is built on top of lower layers
• The bottom layer (layer 0), is the hardware
• The Highest (layer N) is the user interface
• Layers are selected such that each uses functions (operations) and services of only lower-level layers.

Layered Approach

Layered Approach

• Advantages
• Simplicity of construction and debugging
• Disadvantages
• Can be hard to decide how to split functionality into layers
• Less efficient due to high overhead

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