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.
In the [[personal computer]] market, {{as of|20232024|09|lc=y}}, [[Microsoft Windows]] holds a dominant market share of around 6873%. [[macOS]] by [[Apple Inc.]] is in second place (2015%), and the varieties of [[Linux]] is in third place (5%), includingand [[ChromeOS]],are [[Linux distribution|collectively]]is in thirdfourth place (72%).<ref name=":0">{{Cite web |title=Desktop Operating System Market Share Worldwide |url=https://gs.statcounter.com/os-market-share/desktop/worldwide/#monthly-202309-202309-bar |access-date=2023-10-03 |website=StatCounter Global Stats |language=en |archive-date=2 October 2023 |archive-url=https://web.archive.org/web/20231002223546/https://gs.statcounter.com/os-market-share/desktop/worldwide/ |url-status=live }}</ref> In the [[Mobile operating system|mobile]] sector (including [[smartphone]]s and [[Tablet computer|tablets]]), {{as of|2023|09|lc=y}}, [[Android (operating system)|Android's]] share is 68.92%, followed by Apple's [[iOS]] and [[iPadOS]] with 30.42%, and other operating systems with .66%.<ref>{{Cite web |title=Mobile & Tablet Operating System Market Share Worldwide |url=https://gs.statcounter.com/os-market-share/mobile-tablet/worldwide/#monthly-202309-202309-bar |access-date=2023-10-02 |website=StatCounter Global Stats |language=en}}</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|access-date=8 February 2021|archive-date=13 June 2021|archive-url=https://web.archive.org/web/20210613190049/https://www.oreilly.com/library/view/operating-system-concepts/9780471694663/pt07.html|url-status=live}}</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|access-date=8 February 2021|archive-date=14 June 2021|archive-url=https://web.archive.org/web/20210614034001/https://www.acs.eonerc.rwth-aachen.de/cms/E-ON-ERC-ACS/Studium/Lehrveranstaltungen/~lrhs/Spezial-Betriebssysteme/?lidx=1|url-status=live}}</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 (e.g. [[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 flash drive|USB]] stick).
