An operating system (OS) is system software that manages computer hardware and software resources and provides public services for computer programs. Time-sharing operating systems can use the system effectively, and can also include accounting software for processor time, mass storage, printing, and cost allocation of other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between the program and the computer hardware, although application code is usually directly executed by the hardware and often causes the system to call an OS function or be interrupted by it. There are operating systems on many devices, including computers-from mobile phones and video game consoles to network servers and supercomputers.