An operating system is a software interface between you and your computer’s hardware. It manages the hardware found in the computer instead of having the programs handling the hardware. That means the CPU, RAM, GPU, and hard disc are only usable by the operating system. The level of protection of system resources is usually determined by protection rings. Protection rings are a model used to explain the various levels of security of an operating system and what each level can access. For example, Microsoft Windows is a 3 level system of security. Level 0 has access to all hardware resources. On the first level, you have very important drivers such as those for the graphics card. On the second level, you have less important drivers such as the ethernet adapter/wifi car driver. Finally, you have the third level which is the level that third-party software has access to. If a software program wants to access a hardware resource, they must make a system call to use that resource. There are many operating systems that have been developed over time such as the Windows Operating System, the UNIX operating system, Linux, and its various distros. Many operating systems have processes that are switched between simeltanously.