Operating system

An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.

operating system (OS), program that manages a computers resources, especially the allocation of those resources among other programs. Typical resources include the CPU, computer memory file storage, input/output devices, and network connections. Management tasks include scheduling resource use to avoid conflicts and interference between programs. Unlike most programs, which complete a task and terminate, an operating system runs indefinitely and terminates only when the computer is turned off.

Modern multiprocessing operating systems allow many processes to be active, where each process is a “thread” of computation being used to execute a program. One form of multiprocessing is called time- sharing which lets many users share computer access by rapidly switching between them. Time-sharing must guard against interference between users’ programs, and most systems use virtual memory in which the memory, or “address space,” used by a program may reside in secondary memory (such as on a magnetic hard disk drive) when not in immediate use, to be swapped back to occupy the faster main computer memory on demand. This virtual memory both increases the address space available to a program and helps to prevent programs from interfering with each other, but it requires careful control by the operating system and a set of allocation tables to keep track of memory use. Perhaps the most delicate and critical task for a modern operating system is allocation of the CPU; each process is allowed to use the CPU for a limited time, which may be a fraction of a second, and then must give up control and become suspended until its next turn. Switching between processes must itself use the CPU while protecting all data of the processes.