An operating system is a piece of software that most crucially handles the interoperability between hardware and software as well as between different software programs.

In general, an OS is required in order to run other programs. A program that is written to use the hardware directly does not require a separate OS, but this severely limits the possibility of using any other programs in the hardware. Even embedded systems that are only supposed to run a single fixed application often run on top of some kind of an OS.

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