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Operating Systems are like a construction foremen. Users, as the owner of the construction site, issue abstract orders such as Create this file, Open this application, or Browse this website. The operating system is then responsible for translating that abstract order into physical actions. To accomplish these actions, the operating system uses various hardware and software components (such as network controllers, hard drives, monitors, etc.) much like a construction foreman would work with carpenters, electricians, etc. to get the order accomplished.
In addition to taking responsibility for the completion of tasks, the Operating System is also responsible for 'behind the scenes' management tasks. The Operating System also defines system security, much like a construction foreman would say which workers were allowed into which areas of the construction site. Also, the Operating System is responsible for allocating resources in the same manner that the construction foreman would say who gets to use the one crane shared by the entire site, and when (or how) to distribute the limited number of workers to each process.