An
operating system (
OS) is a collection of software that manages
computer hardware resources and provides common services for
computer programs. The operating system is a vital component of the
system software in a computer system. Application programs usually require an operating system to function.
Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting for cost allocation of processor time, mass storage, printing, and other resources.
For hardware functions such as input and output and
memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and will frequently make a
system call to an OS function or be interrupted by it. Operating systems can be found on almost any device that contains a computer—from
cellular phones and
video game consoles to
supercomputers and
web servers.
Examples of popular modern operating systems include
Android,
BSD,
iOS,
GNU/Linux,
Mac OS X,
QNX,
Microsoft Windows,
Windows Phone, and
IBM z/OS. All these, except Windows and z/OS, share roots in
UNIX.