For hardware functions such as [[input and output]] and [[memory allocation]], the operating system acts as an intermediary between programs and the computer hardware,<ref>{{cite book | last = Stallings | title = Operating Systems, Internals and Design Principles | publisher = Prentice Hall | year = 2005 | ___location = Pearson |page=6}}</ref><ref>{{cite book | last = Dhotre| first = I.A.| title = Operating Systems. | publisher = Technical Publications | year = 2009 |page=1}}</ref> although the application code is usually executed directly by the hardware and frequently makes [[system call]]s to an OS function or is [[interrupt]]ed by it. Operating systems are found on many devices that contain a computer{{snd}} from cellular phones and video game consoles to [[web server]]s and [[supercomputer]]s.
{{As of|2023|January}}, the dominant general-purpose desktop operating system is [[Microsoft Windows]] with a market share of around 74.14%. [[macOS]] by [[Apple Inc.]] is in second place (15.33%), and the varieties of [[Linux]] are collectively in third place (2.91%).<ref name="statcounter-desktop">{{cite web|url=https://gs.statcounter.com/os-market-share/desktop/worldwide/#monthly-202301-202301-bar|title=Desktop Operating System Market Share Worldwide|access-date=6 February 2023}}</ref> In the [[Mobile operating system|mobile]] sector, (including smartphonesboth [[smartphone]]s and [[Tablet computer|tablets]]), [[Android (operating system)|Android's]] is dominant with a market share isof 71%, {{asfollowed of|2023|January|lc=y}}.by Apple's [[iOS]] with 28%;<ref name="statcounter-mobile-and-tablet">{{Cite web|title=Mobile & Tablet Operating System Market Share Worldwide|url=https://gs.statcounter.com/os-market-share/mobile-tablet/worldwide/#monthly-202301-202301-bar|access-date=6 February 2023|website=StatCounter Global Stats}}</ref> Accordingfor to third quarter 2016smartphones dataalone, Android'ssharehas on72% smartphonesand is dominant with 87.5 percent with also a growth rate of 10.3 percent per year, followed by Apple's [[iOS]]withhas 12.1 percent with per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent28%.<ref>{{citeCite web |url=http://www.businesswire.com/news/home/20161102006440/en/Strategy-Analytics-Android-Captures-Record-88-Percent |title=StrategyMobile Analytics:Operating AndroidSystem Captures Record 88 PercentMarket Share of Global Smartphone Shipments in Q3 2016 |date=2 November 2016 Worldwide|url-status=live |archive-url=https://webgs.archive.org/web/20161105223332/http://www.businesswirestatcounter.com/newsos-market-share/homemobile/20161102006440worldwide/en/Strategy#monthly-Analytics202301-Android202301-Captures-Record-88-Percent bar|archiveaccess-date=56 NovemberFebruary 20162023|website=StatCounter Global Stats}}</ref> [[Linux distribution]]s are dominant in the server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems)<ref name="auto">{{Cite web|url=https://www.oreilly.com/library/view/operating-system-concepts/9780471694663/pt07.html|title=VII. Special-Purpose Systems - Operating System Concepts, Seventh Edition [Book]|website=www.oreilly.com}}</ref><ref>{{Cite web|url=https://www.acs.eonerc.rwth-aachen.de/cms/E-ON-ERC-ACS/Studium/Lehrveranstaltungen/~lrhs/Spezial-Betriebssysteme/?lidx=1|title=Special-Purpose Operating Systems - RWTH AACHEN UNIVERSITY Institute for Automation of Complex Power Systems - English|website=www.acs.eonerc.rwth-aachen.de}}</ref>), such as [[Embedded system|embedded]] and real-time systems, exist for many applications. [[Security-focused operating system]]s also exist. Some operating systems have low system requirements (i.e. [[light-weight Linux distribution]]). Others may have higher system requirements.
Some operating systems require installation or may come pre-installed with purchased computers ([[OEM]]-installation), whereas others may run directly from media (i.e. [[live cd]]) or flash memory (i.e. usb stick).
