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

programs. All computer programs, excluding firmware, require an operating system to function.

Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software 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 frequently makes system calls to an OS function

or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web

servers and supercomputers.

The dominant desktop operating system is Microsoft Windows with a market share of around 83.3%. macOS by Apple Inc. is in second place (11.2%),

and the varieties of Linux are collectively in third place (1.55%). In the mobile (smartphone and tablet combined) sector, according to third quarter 2016

data, Android by Google is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by iOS by Apple with 12.1 percent and a per

year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent. Linux distributions are dominant in the server

and supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications.