Ø  Structure of operating system –

                                            Structure of operating system                                           

.        GUI- provide interface so that user can interact with system.

2     .       SHELL – Command line interpreter which accept input from user.

3     .       Command processor – receive and execute command.

4      .      Kernel – it is loaded first into memory it is interact with hardware. Which respect the operating system basic function such as management of memory, process, file and input/output device and communication functionality. It also provides all the service requires by user and other parts of operating system.

There are different types of structure of operating system –

1.        Simple structure

2.       Layered structure

3.       Micro kernel

4.      Module approach

5.       Hybrid system

                                            I.            Apple Mac operating system

                                         II.            Apple IOS

                                       III.            Android

       1)      Simple structure -

MS DOS Structure – many operating systems don’t have well defined structure such type of system started as a small simple and limited system. Ms dos is an example of such type of system in ms dos, the interface and levels of functionality are not well separated.

          

·         Like ms dos and UNIX was also limited by hardware functionality it consists of two separate parts.

I         kernel

II       system program

·         The kernel provides the file system, CPU scheduling memory management and other operating system of functions through system calls.

        2)     Layered structure –

·         In layered approach operating system is broken into number of layer (level) the bottom layer is hardware and highest layer is user interface.

·         The main advantage of layered approach is simplicity of construction and debugging.

·         the major difficulty in this approach is that appropriately defining various layer because a layer can use only lower level layer careful planning necessary.

         3)     Microkernel approach –

·         In microkernel approach develop an operating system called Mac.

·         This method structure removing all nonessential components from the kernel and implementing them operating system and user level programs.

·         So the result is smaller kernel.

·         Micro kernel provides minimal process and memory management.

·         The main function of micro kernel is to provide communication between the client program and the various services that are also running in user space.

·         Communication is provided through message passing.

·         Benefit of micro kernel approach is that it make extending the operating system easier

·         Also provide more security and reliability.

·         Qnx (real-time os) and Windows NT follow this approach.