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operating system
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{{pp-vandalism|small=yes}}{{pp-move-indef}}{{Use dmy dates|date=July 2015}}{{OS}}An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.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,BOOK, Stallings, Operating Systems, Internals and Design Principles, Prentice Hall, 2005, Pearson, 6, BOOK, Dhotre, I.A., Operating Systems., Technical Publications, 2009, 1, 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{{snd}} 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 82.74%. macOS by Apple Inc. is in second place (13.23%), and the varieties of Linux are collectively in third place (1.57%).WEB,weblink Desktop Operating System Market Share Worldwide {{!, StatCounter Global Stats|website=StatCounter Global Stats|language=en|access-date=2017-12-18}} In the mobile (including smartphones and tablets) sector, Google Android's share is up to 70% in the year 2017.WEB,weblink Mobile & Tablet Operating System Market Share Worldwide {{!, StatCounter Global Stats|website=StatCounter Global Stats|language=en|access-date=2017-12-18}} According to third quarter 2016 data, Android's share on smartphones is dominant with 87.5 percent with also a growth rate of 10.3 percent per year, followed by Apple's iOS with 12.1 percent with per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.WEB,weblink Strategy Analytics: Android Captures Record 88 Percent Share of Global Smartphone Shipments in Q3 2016, November 2, 2016, live,weblink" title="">weblink 5 November 2016, dmy-all, 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.

Types of operating systems

Single-tasking and multi-tasking


Single- and multi-user



A distributed operating system manages a group of distinct computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they form a distributed system.BOOK, Mishra, B., Singh, N., Singh, R., Master-slave group based model for co-ordinator selection, an improvement of bully algorithm, International Conference on Parallel, Distributed and Grid Computing (PDGC), 2014, 457â€“460, 10.1109/PDGC.2014.7030789, 978-1-4799-7682-9,


In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system, then saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, and is common in large server warehouses.BOOK, 978-1118063330, Operating Systems Concepts, Gagne, Silberschatz Galvin, 716, New York, Wiley, 2012,








{{See also|Resident monitor}}Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their modern and more complex forms until the early 1960s.BOOK, Classic Operating Systems, Per Brinch, Hansen, 2001, Springer, 0-387-95113-X, 4â€“7,weblink Hardware features were added, that enabled use of runtime libraries, interrupts, and parallel processing. When personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers.In the 1940s, the earliest electronic digital systems had no operating systems. Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the printing of payroll checks from data on punched paper cards. After programmable general purpose computers were invented, machine languages (consisting of strings of the binary digits 0 and 1 on punched paper tape) were introduced that sped up the programming process (Stern, 1981).{{Full citation needed|date=August 2014}}File:IBM360-65-1.corestore.jpg|thumb|OS/360 was used on most IBM mainframe computers beginning in 1966, including computers used by the Apollo programApollo programIn the early 1950s, a computer could execute only one program at a time. Each user had sole use of the computer for a limited period of time and would arrive at a scheduled time with program and data on punched paper cards or punched tape. The program would be loaded into the machine, and the machine would be set to work until the program completed or crashed. Programs could generally be debugged via a front panel using toggle switches and panel lights. It is said that Alan Turing was a master of this on the early Manchester Mark 1 machine, and he was already deriving the primitive conception of an operating system from the principles of the universal Turing machine.Later machines came with libraries of programs, which would be linked to a user's program to assist in operations such as input and output and generating computer code from human-readable symbolic code. This was the genesis of the modern-day operating system. However, machines still ran a single job at a time. At Cambridge University in England the job queue was at one time a washing line (clothes line) from which tapes were hung with different colored clothes-pegs to indicate job-priority.{{citation needed|date=September 2010}}An improvement was the Atlas Supervisor introduced with the Manchester Atlas commissioned in 1962, "considered by many to be the first recognisable modern operating system".BOOK, Lavington, Simon, A History of Manchester Computers, 1998, 2nd, The British Computer Society, Swindon, 978-1-902505-01-5, 50â€“52, Brinch Hansen described it as "the most significant breakthrough in the history of operating systems."BOOK, Brinch Hansen, Per, Classic Operating Systems: From Batch Processing to Distributed Systems, 2000, Springer-Verlag,






Unix and Unix-like operating systems

File:Unix history-simple.png|256px|thumb|Evolution of Unix systemsdefault (File:Unix history-simple.svg)Unix was originally written in assembly language.WEB, Ritchie, Dennis, Unix Manual, first edition,weblink Lucent Technologies, 22 November 2012, dead,weblink" title="">weblink 18 May 2008, dmy-all, Ken Thompson wrote B, mainly based on BCPL, based on his experience in the MULTICS project. B was replaced by C, and Unix, rewritten in C, developed into a large, complex family of inter-related operating systems which have been influential in every modern operating system (see History).The Unix-like family is a diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group which licenses it for use with any operating system that has been shown to conform to their definitions. "UNIX-like" is commonly used to refer to the large set of operating systems which resemble the original UNIX.Unix-like systems run on a wide variety of computer architectures. They are used heavily for servers in business, as well as workstations in academic and engineering environments. Free UNIX variants, such as Linux and BSD, are popular in these areas.Four operating systems are certified by The Open Group (holder of the Unix trademark) as Unix. HP's HP-UX and IBM's AIX are both descendants of the original System V Unix and are designed to run only on their respective vendor's hardware. In contrast, Sun Microsystems's Solaris can run on multiple types of hardware, including x86 and Sparc servers, and PCs. Apple's macOS, a replacement for Apple's earlier (non-Unix) Mac OS, is a hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD.Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants.

BSD and its descendants





File:Ubuntu 19.04 "Disco Dingo".png|thumb|250px|Ubuntu, desktop Linux distributionLinux distributionThe Linux kernel originated in 1991, as a project of Linus Torvalds, while a university student in Finland. He posted information about his project on a newsgroup for computer students and programmers, and received support and assistance from volunteers who succeeded in creating a complete and functional kernel.Linux is Unix-like, but was developed without any Unix code, unlike BSD and its variants. Because of its open license model, the Linux kernel code is available for study and modification, which resulted in its use on a wide range of computing machinery from supercomputers to smart-watches. Although estimates suggest that Linux is used on only 1.82% of all "desktop" (or laptop) PCs,WEB, Top 5 Operating Systems from January to April 2011,weblink StatCounter, October 2009, 5 November 2009, live,weblink" title="">weblink 26 May 2012, dmy-all, it has been widely adopted for use in serversWEB,weblink IDC report into Server market share,, 2012-08-07, dead,weblink" title="">weblink 27 September 2012, dmy-all, and embedded systemsWEB, LinuxDevices Staff, Linux still top embedded OS,weblink 23 April 2008,, 5 April 2016, dead,weblink" title="">weblink 19 April 2016, dmy-all, such as cell phones. Linux has superseded Unix on many platforms and is used on most supercomputers including the top 385.WEB,weblink Sublist Generator,, 6 February 2017, Many of the same computers are also on Green500 (but in different order), and Linux runs on the top 10. Linux is also commonly used on other small energy-efficient computers, such as smartphones and smartwatches. The Linux kernel is used in some popular distributions, such as Red Hat, Debian, Ubuntu, Linux Mint and Google's Android, Chrome OS, and Chromium OS.

Microsoft Windows

Microsoft Windows is a family of proprietary operating systems designed by Microsoft Corporation and primarily targeted to Intel architecture based computers, with an estimated 88.9 percent total usage share on Web connected computers.NEWS, Global Web Stats,weblink May 2011, Net Market Share, Net Applications, 2011-05-07, live,weblink" title="">weblink 25 January 2010, dmy-all, NEWS, Global Web Stats,weblink September 2009, W3Counter, Awio Web Services, 2009-10-24, live,weblink" title="">weblink 28 June 2012, dmy-all, WEB, Operating System Market Share,weblink Net Applications, October 2009, 5 November 2009, live,weblink" title="">weblink 25 January 2010, dmy-all, The latest version is Windows 10.In 2011, Windows 7 overtook Windows XP as most common version in use.WEB, OS Platform Statistics,weblink 30 October 2011, live,weblink" title="">weblink 5 August 2011, dmy-all, WEB, Stats Count Global Stats Top Five Operating Systems,weblink 30 October 2011, live,weblink" title="">weblink 26 May 2012, dmy-all, WEB, Global statistics at,weblink 23 January 2012, live,weblink" title="">weblink 28 June 2012, dmy-all, Microsoft Windows was first released in 1985, as an operating environment running on top of MS-DOS, which was the standard operating system shipped on most Intel architecture personal computers at the time. In 1995, Windows 95 was released which only used MS-DOS as a bootstrap. For backwards compatibility, Win9x could run real-mode MS-DOSWEB,weblink Troubleshooting MS-DOS Compatibility Mode on Hard Disks,, 2012-08-07, live,weblink" title="">weblink 10 August 2012, dmy-all, WEB,weblink Using NDIS 2 PCMCIA Network Card Drivers in Windows 95,, 2012-08-07, live,weblink" title="">weblink 17 February 2013, dmy-all, and 16-bit Windows 3.xWEB,weblink INFO: Windows 95 Multimedia Wave Device Drivers Must be 16 bit,, 2012-08-07, live,weblink" title="">weblink 17 February 2013, dmy-all, drivers. Windows ME, released in 2000, was the last version in the Win9x family. Later versions have all been based on the Windows NT kernel. Current client versions of Windows run on IA-32, x86-64 and 32-bit ARM microprocessors.NEWS, Arthur, Charles, Windows 8 will run on ARM chips - but third-party apps will need rewrite,weblink The Guardian, live,weblink 12 October 2016, dmy-all, In addition Itanium is still supported in older server version Windows Server 2008 R2. In the past, Windows NT supported additional architectures.Server editions of Windows are widely used. In recent years, Microsoft has expended significant capital in an effort to promote the use of Windows as a server operating system. However, Windows' usage on servers is not as widespread as on personal computers as Windows competes against Linux and BSD for server market share.WEB,weblink Operating System Share by Groups for Sites in All Locations January 2009, live,weblink" title="">weblink 6 July 2009, dmy-all, NEWS,weblink Behind the IDC data: Windows still No. 1 in server operating systems, 2010-02-26, ZDNet, live,weblink" title="">weblink 1 March 2010, dmy-all, ReactOS is a Windows-alternative operating system, which is being developed on the principles of Windows{{snd}} without using any of Microsoft's code.







Program execution






Memory management


Virtual memory

{{Further|Page fault}}(File:Virtual memory.svg|thumb|250px|Many operating systems can "trick" programs into using memory scattered around the hard disk and RAM as if it is one continuous chunk of memory, called virtual memory.)The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks.If a program tries to access memory that isn't in its current range of accessible memory, but nonetheless has been allocated to it, the kernel is interrupted in the same way as it would if the program were to exceed its allocated memory. (See section on memory management.) Under UNIX this kind of interrupt is referred to as a page fault.When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where a particular application's memory is stored, or even whether or not it has actually been allocated yet.In modern operating systems, memory which is accessed less frequently can be temporarily stored on disk or other media to make that space available for use by other programs. This is called swapping, as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand."Virtual memory" provides the programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there.BOOK, Stallings, William, Computer Organization & Architecture, 2008, Prentice-Hall of India Private Limited, New Delhi, 978-81-203-2962-1, 267,



Disk access and file systems


Device drivers






User interface


Graphical user interfaces

File:KDE Plasma 5.16.png|thumb|left|256px|A screenshot of the KDE Plasma 5KDE Plasma 5Most of the modern computer systems support graphical user interfaces (GUI), and often include them. In some computer systems, such as the original implementation of the classic Mac OS, the GUI is integrated into the kernel.While technically a graphical user interface is not an operating system service, incorporating support for one into the operating system kernel can allow the GUI to be more responsive by reducing the number of context switches required for the GUI to perform its output functions. Other operating systems are modular, separating the graphics subsystem from the kernel and the Operating System. In the 1980s UNIX, VMS and many others had operating systems that were built this way. Linux and macOS are also built this way. Modern releases of Microsoft Windows such as Windows Vista implement a graphics subsystem that is mostly in user-space; however the graphics drawing routines of versions between Windows NT 4.0 and Windows Server 2003 exist mostly in kernel space. Windows 9x had very little distinction between the interface and the kernel.Many computer operating systems allow the user to install or create any user interface they desire. The X Window System in conjunction with GNOME or KDE Plasma 5 is a commonly found setup on most Unix and Unix-like (BSD, Linux, Solaris) systems. A number of Windows shell replacements have been released for Microsoft Windows, which offer alternatives to the included Windows shell, but the shell itself cannot be separated from Windows.Numerous Unix-based GUIs have existed over time, most derived from X11. Competition among the various vendors of Unix (HP, IBM, Sun) led to much fragmentation, though an effort to standardize in the 1990s to COSE and CDE failed for various reasons, and were eventually eclipsed by the widespread adoption of GNOME and K Desktop Environment. Prior to free software-based toolkits and desktop environments, Motif was the prevalent toolkit/desktop combination (and was the basis upon which CDE was developed).Graphical user interfaces evolve over time. For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 1999.Poisson, Ken. "Chronology of Personal Computer Software" {{webarchive|url= |date=14 May 2008 }}. Retrieved on 2008-05-07. Last checked on 2009-03-30.

Real-time operating systems

A real-time operating system (RTOS) is an operating system intended for applications with fixed deadlines (real-time computing). Such applications include some small embedded systems, automobile engine controllers, industrial robots, spacecraft, industrial control, and some large-scale computing systems.An early example of a large-scale real-time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System.Embedded systems that have fixed deadlines use a real-time operating system such as VxWorks, PikeOS, eCos, QNX, MontaVista Linux and RTLinux. Windows CE is a real-time operating system that shares similar APIs to desktop Windows but shares none of desktop Windows' codebase.WEB,weblink Reading: Operating System, Lumen, 5 January 2019, Symbian OS also has an RTOS kernel (EKA2) starting with version 8.0b.Some embedded systems use operating systems such as Palm OS, BSD, and Linux, although such operating systems do not support real-time computing.

Operating system development as a hobby

{{See also|Hobbyist operating system development}}Operating system development is one of the most complicated activities in which a computing hobbyist may engage.{{citation needed|date=February 2015}} A hobby operating system may be classified as one whose code has not been directly derived from an existing operating system, and has few users and active developers.WEB
, Osnews
, My OS is less hobby than yours
, 21 December 2009
, 21 December 2009
, live
,weblink" title="">weblink
, 24 December 2009
, dmy-all

Diversity of operating systems and portability

Application software is generally written for use on a specific operating system, and sometimes even for specific hardware.{{Citation needed|date = April 2015}} When porting the application to run on another OS, the functionality required by that application may be implemented differently by that OS (the names of functions, meaning of arguments, etc.) requiring the application to be adapted, changed, or otherwise maintained.Unix was the first operating system not written in assembly language, making it very portable to systems different from its native PDP-11.NEWS,weblink The History of Unix, BYTE, August 1983, 31 January 2015, 188, This cost in supporting operating systems diversity can be avoided by instead writing applications against software platforms such as Java or Qt. These abstractions have already borne the cost of adaptation to specific operating systems and their system libraries.Another approach is for operating system vendors to adopt standards. For example, POSIX and OS abstraction layers provide commonalities that reduce porting costs.

Market share

{{Further|Usage share of operating systems}}

See also

{{div col}} {{div col end}}



Further reading

  • JOURNAL, Auslander, Marc A., Larkin, David C., Scherr, Allan L., The evolution of the MVS Operating System, IBM J. Research & Development, 1981,weblink
  • BOOK, Deitel, Harvey M., Deitel, Paul, Choffnes, David, Operating Systems, Pearson/Prentice Hall, 978-0-13-092641-8,
  • BOOK, Bic, Lubomur F., Shaw, Alan C., Operating Systems, Prentice Hall, 2003, Pearson,
  • BOOK, Silberschatz, Avi, Galvin, Peter, Gagne, Greg, Operating Systems Concepts, John Wiley & Sons, 2008, 0-470-12872-0,
  • O'Brien, J. A., & Marakas, G. M.(2011). Management Information Systems. 10e. McGraw-Hill Irwin.
  • BOOK, Leva, Alberto, Maggio, Martina, Papadopoulos, Alessandro Vittorio, Terraneo, Federico, Control-based Operating System Design, Institution of Engineering and Technology, IET, 2013, 978-1-84919-609-3,
  • BOOK, Arpaci-Dusseau, Remzi, Arpaci-Dusseau, Andrea, 2015,weblink Operating Systems: Three Easy Pieces,

External links

{{Wiktionary}}{{Commons category|Screenshots by operating system|Screenshots of operating systems}}{{Wikiversity|Operating Systems}}
  • {{curlie|Computers/Software/Operating_Systems|Operating Systems}}
  • Multics History and the history of operating systems
{{Operating system}}{{Systems science}}{{Computer science}}{{Authority control}}

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