An operating system (OS) is the low-level software which handles the interface to peripheral hardware, schedules tasks, allocates storage, and presents a default interface to the user when no application program is running.
The OS may be split into a kernel which is always present and various system programs which use facilities provided by the kernel to perform higher-level house-keeping tasks, often acting as servers in a client-server relationship.
Some may include a graphical user interface and window system as part of the OS, while others may rely on a command-line interface. The operating system loader, BIOS, or other firmware required at boot time or when installing the operating system would generally not be considered part of the operating system, though this distinction is unclear in the case of a ROM-based operating system such as RISC OS.
The facilities an operating system provides and its general design philosophy exert an extremely strong influence on programming style and on the technical cultures that grow up around the machines on which it runs.
Operating system examples
- Chrome OS
- Mach (foundation of NeXTSTEP)
- Microsoft Windows
- NeXTSTEP (predecessor to Mac OS X)
Operating systems from Apple
- macOS (formerly Mac OS X, replaced classic Mac OS)
- iOS (formerly iPhone OS, developed from Mac OS X)
- iPadOS (developed from iOS)
- watchOS (developed from iOS)
- tvOS (developed from iOS)