Internal structure of operating systems can differ. Structures of operating systems tend to differ depending on the arrangement of files, how hardware and applications are installed and controlled and how the user interacts with the system. When it comes to Macintosh, Windows, Linux, and other operating systems, their performance depends on it structure, as different operating systems were built with different concepts and uses in mind.
MS DOS has the simplest structure. It was written with the aim of providing more functionality in less space. It is not separated into modules. Though MS-DOS does have some structure, the interface of MS-DOS and the levels of functionality are not clearly separated. MS-DOS follows a layered approach. MS-DOS operating systems are divided into a number of layers; build one on top of the other. The bottom layer, layer 0, contains hardware and the highest layer is known as the user interface. Layers are chosen with modularity so that each utilizes services and operations of only the immediate lower-level.
UNIX operating systems has limited structuring. It has two separate parts as System programs & The Kernel. The UNIX operating system consists of everything below the system interface and above the physical layer (hardware). It provides a large number of functions for one level like file system, CPU scheduling, memory management and other operating system functions.
The modern operating systems implement kernel modules. This is structured using object-oriented approaches. Each core component is separate and talks to each other over known interfaces. Each core component is loadable as and when needed within the kernel. Overall it is similar to the layered architecture but with more flexibility.
Virtual machines are structured by taking the layered approach to the most logical conclusion. Virtual machines treat hardware's and the kernel of the operating system as though all are hardware. Virtual machines provide interfaces matching the underlying hardware. Operating systems generates the vision of multiple processes, all executing on its very own processor with its very own virtual memory. It is structured in a manner that the resources of the physical computer are shared to make the virtual machine. CPU scheduling creates the idea that users have their own processor. A normal user time -sharing terminal serves as the virtual machine operator's console.
These are some basic structures of operating systems. One can identify ways in which they are alike and differ according to the purpose it was built to serve. The architectures differ with technological advances, outdating techniques frequently.