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In this video we will see operating system structure.  There are two common structures 

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monolithic structure and microkernels.

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An operating system typically contains scheduling, memory management and system call interface etc 

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.

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In monolithic system structure, the entire operating system runs as a large executable program in kernel mode. 

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So we can think all these modules as a single one. In this system structure, calling any function is simple

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.

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All we need to do is find the correct function which we need and call that function.

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So it is direct communication between modules and calling any function is efficient.  

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But free to call any function without restrictions makes the system hard to maintain and any module having errors will affect 

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the entire operating system.

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For example, if we encounter an error in memory management module, we will halt the whole system.

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Another structure is microkernel structure.  In this structure, operating system is divided into small modules 

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which runs in user mode. 

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As you can see, the modules run as separate processes in the user mode.

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The microkernel which schedules processes, 

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manage communications between these processes are running in the kernel mode.  

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So the kernel is really small.

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Any error in those modules will only affect themselves and will not crash the whole system. 

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In this course, we will write a monolithic kernel. The main reason is that the kernel we will write 

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is really small and implementing a monolithic kernel is easy to understand and simple to do comparing to microkernel

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.

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In the next lecture, we will start writing our own operating system. See you in the next section.