Structure of Operating System

The design of an operating system is very complex task. To reduce the complexity, operating systems are usually designed and implemented in the form of hierarchy of layers. The layered architecture provides abstraction where most complex details are confined within modules. The basic idea in designing an operating system is to create hierarchy of levels of abstractions so that at each level the details of operation of lower levels may be ignored. Each level of abstraction provides a set of objects and related set of operations that maybe used by higher levels. A hierarchical operating system model is shown below,

General Structure of an Operating System

Layer 1

Kernel uses only the objects and operations provided by the hardware. The typical functions include in the operating system kernel are

·        Interrupt process mechanism

·        Memory protection

·        Memory swapping

·        Virtual memory management

·        Inter-process communication

·        Network mechanisms

·        I/O management

·        Process management

Layer 2

Main function of layer 2 is provide functionalities for management of secondary storage devices. Layer 2 also provide some functionalities for swapping.

Layer 3

Memory management functions of operating system are implemented in this layer. It allocates memory for programs to be loaded , and frees it when it is no longer needed. Virtual memory management is another function of this layer. Modules of layer 3 handle hardware interrupts that signal attempts to address data not in memory. In this case layer 3 use functions of layer 2 to brought missing blocks from secondary storage to primary memory.

Layer 4

Information management functions of operating system are implemented in this layer. More sophisticated forms of space allocation and accessing of data on secondary storage than those provided by layer 2 are implemented at layer 4. Layer 4 also manages external devices and peripherals, such as printer and terminals.

Layer 5

Layer 5 provides an interface between interactive users and operating system. Modules at layer 5 use the facilities provided by the lower levels to accept command line from terminals. Modern operating systems are use Graphical User Interface (GUI), GUI provide a graphical environment for users to communicate with operating system. 

NEXT: Bootstrapping 

Previous: Introduction to operating system

Index : Operating System