Windows is a

product line In marketing jargon, product lining refers to the offering of several related product (business), products for individual sale. Unlike product bundling, where several products are combined into one group, which is then offered for sale as a uni ...

of proprietary graphical

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s developed and marketed by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

. It is grouped into families and subfamilies that cater to particular sectors of the computing industry – Windows (unqualified) for a consumer or corporate

workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating syste ...

Windows Server Windows Server (formerly Windows NT Server) is a brand name for Server (computing), server-oriented releases of the Windows NT operating system (OS) that have been developed by Microsoft since 1993. The first release under this brand name i ...

for a server and Windows IoT for an

embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...

. Windows is sold as either a consumer

retail Retail is the sale of goods and services to consumers, in contrast to wholesaling, which is the sale to business or institutional customers. A retailer purchases goods in large quantities from manufacturers, directly or through a wholes ...

product or licensed to third-party hardware manufacturers who sell products bundled with Windows. The first version of Windows, Windows 1.0, was released on November 20, 1985, as a graphical operating system shell for

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

in response to the growing interest in

graphical user interface A graphical user interface, or GUI, is a form of user interface that allows user (computing), users to human–computer interaction, interact with electronic devices through Graphics, graphical icon (computing), icons and visual indicators such ...

s (GUIs). The name "Windows" is a reference to the windowing system in GUIs. The 1990 release of Windows 3.0 catapulted its market success and led to various other product families, including the now-defunct

Windows 9x Windows 9x is a generic term referring to a line of discontinued Microsoft Windows operating systems released from 1995 to 2000 and supported until 2006, which were based on the kernel introduced in Windows 95 and modified in succeeding version ...

Windows Mobile Windows Mobile is a discontinued mobile operating system developed by Microsoft for smartphones and personal digital assistants (PDA). Designed to be the portable equivalent of the Windows desktop OS in the emerging Mobile device, mobile/port ...

Windows Phone Windows Phone (WP) is a discontinued mobile operating system developed by Microsoft Mobile for smartphones as the replacement successor to Windows Mobile and Zune. Windows Phone featured a new user interface derived from the Metro design languag ...

, and Windows CE/Embedded Compact. Windows is the most popular desktop operating system in the world, with a 70%

market share Market share is the percentage of the total revenue or sales in a Market (economics), market that a company's business makes up. For example, if there are 50,000 units sold per year in a given industry, a company whose sales were 5,000 of those ...

, according to StatCounter; however when including

mobile operating system A mobile operating system is an operating system used for smartphones, tablets, smartwatches, smartglasses, or other non-laptop personal mobile computing devices. While computers such as laptops are "mobile", the operating systems used on the ...

s, it is in second place, behind Android. The most recent version of Windows is

Windows 11 Windows 11 is a version of Microsoft's Windows NT operating system, released on October 5, 2021, as the successor to Windows 10 (2015). It is available as a free upgrade for devices running Windows 10 that meet the #System requirements, Windo ...

for consumer PCs and tablets, Windows 11 Enterprise for corporations, and

Windows Server 2025 Windows Server 2025 is the fourteenth and current major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server brand name. It was released on November 1, 2024. Microsoft announced that the su ...

for servers. Still supported are some editions of

Windows 10 Windows 10 is a major release of Microsoft's Windows NT operating system. The successor to Windows 8.1, it was Software release cycle#Release to manufacturing (RTM), released to manufacturing on July 15, 2015, and later to retail on July 2 ...

, Windows Server 2016 or later (and exceptionally with paid support down to

Windows Server 2008 Windows Server 2008, codenamed "Longhorn Server" (alternatives: "Windows Vista Server" or "Windows Server Vista"), is the seventh major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server b ...

Product line

the only active top-level family is

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

. The first version, Windows NT 3.1, was intended for server computing and corporate

workstations A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating systems. The term ''workstat ...

. It grew into a product line of its own and now consists of four sub-families that tend to be released almost simultaneously and share the same kernel. * Windows (unqualified): For a consumer or corporate

or tablet. The latest version is

. Its main competitors are

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

and

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

for personal computers and

iPadOS iPadOS is a mobile operating system developed by Apple for its iPad line of tablet computers. It was given a name distinct from iOS, the operating system used by Apple's iPhones to reflect the diverging features of the two product lines, suc ...

and Android for tablets (cf. ). **''Of note: "Windows" refers to both the overall product line and this sub-family of it.'' *

: For a server computer. The latest version is

. Unlike its client sibling, it has adopted a strong naming scheme. The main competitor of this family is

. (cf. ) * Windows PE: A lightweight version of its Windows sibling, meant to operate as a live operating system, used for installing Windows on bare-metal computers (especially on many computers at once), recovery, or troubleshooting purposes. The latest version is Windows PE 10. * Windows IoT (previously Windows Embedded): For IoT and embedded computers. The latest version is Windows 11 IoT Enterprise. Like Windows Server, the main competitor of this family is Linux. (cf. ) These top-level Windows families are no longer actively developed: *

: Intended exclusively for the consumer market. The first version was

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

, which was followed by

Windows 98 Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the second operating system in the 9x line, as the successor to Windows 95. It was Software ...

. The last version of the Windows 9x family was

Windows Me Windows Me (Millennium Edition) is an operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the successor to Windows 98, and was released to manufacturing on June 19, 2000, and t ...

, which was widely regarded as one of the worst operating systems of all time, with ''

PC World ''PC World'' (stylized as PCWorld) is a global computer magazine published monthly by IDG. Since 2013, it has been an online-only publication. It offers advice on various aspects of PCs and related items, the Internet, and other personal tec ...

'' labeling it as "Mistake Edition" and placing it 4th in their list of ''Worst Tech Products'' in 2006). All versions of the Windows 9x family have a

monolithic kernel A monolithic kernel is an operating system software architecture, architecture with the entire operating system running in kernel space. The monolithic model differs from other architectures such as the microkernel in that it alone defines a high ...

that uses

as a foundation alongside the kernel first used with Windows 95. This line has since been defunct, with Microsoft now catering to the consumer market with Windows NT starting with

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct successor to Windows 2000 for high-end and business users a ...

. *

: The predecessor to Windows Phone, a mobile phone and PDA operating system. The first version was called Pocket PC 2000. The third version, Windows Mobile 2003, was the first version to adopt the Windows Mobile trademark. The last published version was Windows Mobile 6.5. *

: Sold only to smartphone manufacturers. The first version was Windows Phone 7, followed by

Windows Phone 8 Windows Phone 8 is the second generation of the Windows Phone mobile operating system from Microsoft Corporation, Microsoft, released on October 29, 2012. It runs on the Windows NT kernel and is the successor to Windows Phone 7. It was the first ...

and Windows Phone 8.1. It was succeeded by Windows 10 Mobile, which is also defunct. *

Windows Embedded Compact Windows CE, later known as Windows Embedded CE and Windows Embedded Compact, is a discontinued operating system developed by Microsoft for Mobile device, mobile and Embedded system, embedded devices. It was part of the Windows Embedded family an ...

: Most commonly known by its former name, Windows CE, it is a

hybrid kernel A hybrid kernel is an operating system Kernel (operating system), kernel whose architecture attempts to combine aspects and benefits of microkernel and monolithic kernel architectures used in operating systems. Overview The traditional kernel cat ...

operating system optimized for low power and memory systems, with OEMs able to modify the UI to suit their needs. The final version was Windows Embedded Compact 2013, and it is succeeded by Windows IoT.

History

The term ''Windows'' collectively describes any or all of several generations of

products. These products are generally categorized as follows:

Early versions

The history of Windows dates back to 1981 when Microsoft started work on a program called "Interface Manager". The name "Windows" comes from the fact that the system was one of the first to use graphical boxes to represent programs; in the industry, at the time, these were called "windows" and the underlying software was called "windowing software." It was announced in November 1983 (after the

Apple Lisa Lisa is a desktop computer developed by Apple, produced from January 19, 1983, to August 1, 1986, and succeeded by Macintosh. It is generally considered the first mass-market personal computer operable through a graphical user interface (GUI). I ...

, but before the

Macintosh Mac is a brand of personal computers designed and marketed by Apple Inc., Apple since 1984. The name is short for Macintosh (its official name until 1999), a reference to the McIntosh (apple), McIntosh apple. The current product lineup inclu ...

) under the name "Windows", but Windows 1.0 was not released until November 1985. Windows 1.0 was to compete with

's operating system, but achieved little popularity. Windows 1.0 is not a complete operating system; rather, it extends

. The shell of Windows 1.0 is a program known as the MS-DOS Executive. Components included

Calculator An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics. The first solid-state electronic calculator was created in the early 1960s. Pocket-si ...

, Calendar, Cardfile, Clipboard Viewer, Clock, Control Panel,

Notepad A notebook (also known as a notepad, writing pad, drawing pad, or legal pad) is a book or stack of paper pages that are often Ruled paper, ruled and used for purposes such as note-taking, Diary, journaling or other writing, drawing, or scrapbooki ...

Paint Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...

, Reversi, Terminal and

Write Writing is the act of creating a persistent representation of language. A writing system includes a particular set of symbols called a ''script'', as well as the rules by which they encode a particular spoken language. Every written language ...

. Windows 1.0 does not allow overlapping windows. Instead, all windows are tiled. Only modal dialog boxes may appear over other windows. Microsoft sold as included Windows Development libraries with the C development environment, which included numerous windows samples. Windows 2.0 was released in December 1987, and was more popular than its predecessor. It features several improvements to the user interface and memory management. Windows 2.03 changed the OS from tiled windows to overlapping windows. The result of this change led to Apple Computer filing a suit against Microsoft alleging infringement on Apple's copyrights (eventually settled in court in Microsoft's favor in 1993). Windows 2.0 also introduced more sophisticated

keyboard shortcut In computing, a keyboard shortcut (also hotkey/hot key or key binding) is a software-based assignment of an action to one or more keys on a computer keyboard. Most Operating system, operating systems and Application software, applications come ...

s and could make use of

expanded memory In DOS memory management, expanded memory is a system of bank switching that provided additional memory to DOS programs beyond the limit of conventional memory (640 KiB). ''Expanded memory'' is an umbrella term for several incompatible tech ...

. Windows 2.1 was released in two different versions: Windows/286 and Windows/386. Windows/386 uses the

virtual 8086 mode In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running ...

of the

Intel 80386 The Intel 386, originally released as the 80386 and later renamed i386, is the third-generation x86 architecture microprocessor from Intel. It was the first 32-bit computing, 32-bit processor in the line, making it a significant evolution in ...

to multitask several DOS programs and the paged memory model to emulate expanded memory using available extended memory. Windows/286, in spite of its name, runs on both

Intel 8086 The 8086 (also called iAPX 86) is a 16-bit computing, 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-b ...

and

Intel 80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also the f ...

processors. It runs in

real mode Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20- bit s ...

but can make use of the

high memory area In DOS memory management, the high memory area (HMA) is the RAM area consisting of the first 65520 bytes above the one megabyte in an IBM AT or compatible computer. In real mode, the segmentation architecture of the Intel 8086 and subseque ...

. In addition to full Windows packages, there were runtime-only versions that shipped with early Windows software from third parties and made it possible to run their Windows software on MS-DOS and without the full Windows feature set. The early versions of Windows are often thought of as graphical shells, mostly because they ran on top of MS-DOS and used it for file system services. However, even the earliest Windows versions already assumed many typical operating system functions; notably, having their own executable file format and providing their own

device driver In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...

s (timer, graphics, printer, mouse, keyboard and sound). Unlike MS-DOS, Windows allowed users to execute multiple graphical applications at the same time, through

cooperative multitasking Cooperative multitasking, also known as non-preemptive multitasking, is a computer multitasking technique in which the operating system never initiates a context switch from a running Process (computing), process to another process. Instead, in o ...

. Windows implemented an elaborate, segment-based, software virtual memory scheme, which allows it to run applications larger than available memory: code segments and

resources ''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...

are swapped in and thrown away when memory became scarce; data segments moved in memory when a given application had relinquished processor control.

Windows 3.x

Windows 3.0, released in 1990, improved the design, mostly because of

virtual memory In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a ver ...

and loadable virtual device drivers ( VxDs) that allow Windows to share arbitrary devices between multi-tasked DOS applications. Windows 3.0 applications can run in

protected mode In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as Memory_segmentation, segmentation, virtual mem ...

, which gives them access to several megabytes of memory without the obligation to participate in the software virtual memory scheme. They run inside the same address space, where the segmented memory provides a degree of protection. Windows 3.0 also featured improvements to the user interface. Microsoft rewrote critical operations from C into assembly. Windows 3.0 was the first version of Windows to achieve broad commercial success, selling 2 million copies in the first six months. Microsoft Windows for Workgroups 3

Windows 3.1, made generally available on March 1, 1992, featured a facelift. In October 1992, Windows for Workgroups, a special version with integrated

peer-to-peer networking Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network, forming a peer-to-peer network of nod ...

features, was released. It was sold along with Windows 3.1. Support for Windows 3.1 ended on December 31, 2001. Windows 3.2, released in 1994, is an updated version of the Chinese version of Windows 3.1. The update was limited to this language version, as it fixed only issues related to the complex writing system of the Chinese language. Windows 3.2 was generally sold by computer manufacturers with a ten-disk version of

that also had

Simplified Chinese characters Simplified Chinese characters are one of two standardized Chinese characters, character sets widely used to write the Chinese language, with the other being traditional characters. Their mass standardization during the 20th century was part of ...

in basic output and some translated utilities.

Windows 9x

The next major consumer-oriented release of Windows,

, was released on August 24, 1995. While still remaining MS-DOS-based, Windows 95 introduced support for native 32-bit applications,

plug and play In computing, a plug and play (PnP) device or computer bus is one with a specification that facilitates the recognition of a hardware component in a system without the need for physical device configuration or user intervention in resolving reso ...

hardware, preemptive multitasking,

long file name Long filename (LFN) support is Microsoft's backward-compatible extension of the 8.3 filename (short filename) naming scheme used in MS-DOS. Long filenames can be more descriptive, including longer filename extensions such as .jpeg, .tiff, an ...

s of up to 255 characters, and provided increased stability over its predecessors. Windows 95 also introduced a redesigned,

object oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impleme ...

user interface, replacing the previous

Program Manager Program Manager is the shell of Windows 3.x and Windows NT 3.x operating systems. This shell exposed a task-oriented graphical user interface (GUI), consisting of ''icons'' ( shortcuts for programs) arranged into ''program groups''. It replaced ...

with the Start menu,

taskbar The taskbar is a graphical user interface element that has been part of Microsoft Windows since Windows 95, displaying and facilitating switching between running computer program, programs. The taskbar and the associated Start menu, Start Menu were ...

, and Windows Explorer

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

. Windows 95 was a major commercial success for Microsoft; Ina Fried of CNET remarked that "by the time Windows 95 was finally ushered off the market in 2001, it had become a fixture on computer desktops around the world." Microsoft published four OEM Service Releases (OSR) of Windows 95, each of which was roughly equivalent to a

service pack In computing, a service pack comprises a collection of updates, fixes, or enhancements to a software program delivered in the form of a single installable package. Companies often release a service pack when the number of individual patches to a ...

. The first OSR of Windows 95 was also the first version of Windows to be bundled with Microsoft's

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated as IE or MSIE) is a deprecation, retired series of graphical user interface, graphical web browsers developed by Microsoft that were u ...

. Mainstream support for Windows 95 ended on December 31, 2000, and extended support for Windows 95 ended on December 31, 2001. Windows 95 was followed up with the release of

on June 25, 1998, which introduced the

Windows Driver Model In computing, the Windows Driver Model (WDM) also known at one point as the Win32 Driver Model is a framework for device drivers that was introduced with Windows 98 and Windows 2000 to replace VxD, which was used on older versions of Windows su ...

, support for USB composite devices, support for ACPI,

hibernation Hibernation is a state of minimal activity and metabolic reduction entered by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It is mos ...

, and support for

multi-monitor Multi-monitor, also called multi-display and multi-head, is the use of multiple physical display devices, such as Computer monitor, monitors, Television set, televisions, and Video projector, projectors, in order to increase the area available fo ...

configurations. Windows 98 also included integration with

Internet Explorer 4 Microsoft Internet Explorer 4 (IE4) is the fourth version of the Internet Explorer graphical web browser that Microsoft unveiled in Spring of 1997, and released on September 22, 1997, primarily for Microsoft Windows, but also with versions availa ...

through

Active Desktop Active Desktop was a feature of Microsoft Internet Explorer 4, Internet Explorer 4.0's optional Windows Desktop Update that allowed users to add Hypertext Markup Language, HTML content to the desktop metaphor, desktop, along with some other featu ...

and other aspects of the Windows Desktop Update (a series of enhancements to the Explorer shell which was also made available for Windows 95). In May 1999, Microsoft released Windows 98 Second Edition, an updated version of Windows 98. Windows 98 SE added Internet Explorer 5.0 and

Windows Media Player Windows Media Player (WMP, officially referred to as Windows Media Player Legacy to retronym, distinguish it from Windows Media Player (2022), the new Windows Media Player introduced with Windows 11) is the first media player (application soft ...

6.2 amongst other upgrades. Mainstream support for Windows 98 ended on June 30, 2002, and extended support for Windows 98 ended on July 11, 2006. On September 14, 2000, Microsoft released

(Millennium Edition), the last DOS-based version of Windows. Windows Me incorporated visual interface enhancements from its Windows NT-based counterpart

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...

, had faster boot times than previous versions (which however, required the removal of the ability to access a

DOS environment, removing compatibility with some older programs), expanded

multimedia Multimedia is a form of communication that uses a combination of different content forms, such as Text (literary theory), writing, Sound, audio, images, animations, or video, into a single presentation. T ...

functionality (including Windows Media Player 7,

Windows Movie Maker Windows Movie Maker (known as Windows Live Movie Maker for the 2009 and 2011 releases) is a discontinued video editing software program by Microsoft. It was first included in Windows Me on September 14, 2000, and in Windows XP on October 25, 200 ...

, and the Windows Image Acquisition framework for retrieving images from scanners and digital cameras), additional system utilities such as System File Protection and System Restore, and updated

home network Home Network is a Television in Canada, Canadian English-language Discretionary service, discretionary cable television, cable and satellite television, satellite specialty channel owned by Corus Entertainment. Home Network broadcasts programs r ...

ing tools. However, Windows Me was faced with criticism for its speed and instability, along with hardware compatibility issues and its removal of real mode DOS support. ''

'' considered Windows Me to be one of the worst operating systems Microsoft had ever released, and the fourth worst tech product of all time.

Windows NT

Version history

= Early versions (Windows NT 3.1/3.5/3.51/4.0/2000)

= In November 1988, a new development team within Microsoft (which included former

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...

developers Dave Cutler and Mark Lucovsky) began work on a revamped version of

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

and Microsoft's

OS/2 OS/2 is a Proprietary software, proprietary computer operating system for x86 and PowerPC based personal computers. It was created and initially developed jointly by IBM and Microsoft, under the leadership of IBM software designer Ed Iacobucci, ...

operating system known as "NT OS/2". NT OS/2 was intended to be a secure,

multi-user Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leavi ...

operating system with

POSIX The Portable Operating System Interface (POSIX; ) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines application programming interfaces (APIs), along with comm ...

compatibility and a modular,

portable Portable may refer to: General * Portable building, a manufactured structure that is built off site and moved in upon completion of site and utility work * Portable classroom, a temporary building installed on the grounds of a school to provide a ...

kernel with preemptive multitasking and support for multiple processor architectures. However, following the successful release of Windows 3.0, the NT development team decided to rework the project to use an extended

32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in a maximum of 32- bit units. Compared to smaller bit widths, 32-bit computers can perform la ...

port of the

Windows API The Windows API, informally WinAPI, is the foundational application programming interface (API) that allows a computer program to access the features of the Microsoft Windows operating system in which the program is running. Programs can acces ...

known as Win32 instead of those of OS/2. Win32 maintained a similar structure to the Windows

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

s (allowing existing Windows applications to easily be ported to the platform), but also supported the capabilities of the existing NT kernel. Following its approval by Microsoft's staff, development continued on what was now Windows NT, the first 32-bit version of Windows. However, IBM objected to the changes, and ultimately continued OS/2 development on its own. Windows NT was the first Windows operating system based on a

. The hybrid kernel was designed as a modified

microkernel In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...

, influenced by the Mach microkernel developed by

Richard Rashid Richard Farris Rashid is the founder of Microsoft Research, which he created in 1991. Between 1991 and 2013, as its chief research officer and director, he oversaw the worldwide operations for Microsoft Research which grew to encompass more than ...

at Carnegie Mellon University, but without meeting all of the criteria of a pure microkernel. The first release of the resulting operating system, Windows NT 3.1 (named to associate it with Windows 3.1) was released in July 1993, with versions for desktop

s and servers. Windows NT 3.5 was released in September 1994, focusing on performance improvements and support for

Novell Novell, Inc. () was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as NetWare. Novell technolog ...

NetWare NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol. The final update release was ver ...

, and was followed up by Windows NT 3.51 in May 1995, which included additional improvements and support for the

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

architecture. Windows NT 4.0 was released in June 1996, introducing the redesigned interface of

to the NT series. On February 17, 2000, Microsoft released

, a successor to NT 4.0. The Windows NT name was dropped at this point in order to put a greater focus on the Windows brand.

= Windows XP

= The next major version of Windows NT,

, was released to manufacturing (RTM) on August 24, 2001, and to the general public on October 25, 2001. The introduction of Windows XP aimed to unify the consumer-oriented

series with the architecture introduced by Windows NT, a change which Microsoft promised would provide better performance over its DOS-based predecessors. Windows XP would also introduce a redesigned user interface (including an updated Start menu and a "task-oriented" Windows Explorer), streamlined multimedia and networking features, Internet Explorer 6, integration with Microsoft's .NET Passport services, a " compatibility mode" to help provide

backwards compatibility In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with Input ...

with software designed for previous versions of Windows, and

Remote Assistance Quick Assist is a Microsoft Windows feature that allows a user to view or control a remote Windows computer over a network or the Internet to resolve issues without directly touching the unit. It is based on the Remote Desktop Protocol (RDP). It i ...

functionality. At retail, Windows XP was marketed in two main editions: the "Home" edition was targeted towards consumers, while the "Professional" edition was targeted towards business environments and power users, and included additional security and networking features. Home and Professional were later accompanied by the " Media Center" edition (designed for home theater PCs, with an emphasis on support for DVD playback, TV tuner cards, DVR functionality, and remote controls), and the "Tablet PC" edition (designed for mobile devices meeting its

specifications A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...

for a

tablet computer A tablet computer, commonly shortened to tablet, is a mobile device, typically with a mobile operating system and touchscreen display processing circuitry, and a rechargeable battery in a single, thin and flat package. Tablets, being computers ...

, with support for

stylus A stylus is a writing utensil or tool for scribing or marking into softer materials. Different styluses were used to write in cuneiform by pressing into wet clay, and to scribe or carve into a wax tablet. Very hard styluses are also used to En ...

pen input and additional pen-enabled applications). Mainstream support for Windows XP ended on April 14, 2009. Extended support ended on April 8, 2014. After Windows 2000, Microsoft also changed its release schedules for server operating systems; the server counterpart of Windows XP,

Windows Server 2003 Windows Server 2003, codenamed "Whistler Server", is the sixth major version of the Windows NT operating system produced by Microsoft and the first server version to be released under the Windows Server brand name. It is part of the Windows NT ...

, was released in April 2003. It was followed in December 2005, by Windows Server 2003 R2.

= Windows Vista

= After a lengthy development process,

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

was released on November 30, 2006, for volume licensing and January 30, 2007, for consumers. It contained a number of new features, from a redesigned shell and user interface to significant technical changes, with a particular focus on security features. It was available in a number of different editions, and has been subject to some criticism, such as drop of performance, longer boot time, criticism of new UAC, and stricter license agreement. Vista's server counterpart,

was released in early 2008.

= Windows 7

= On July 22, 2009,

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...

and

Windows Server 2008 R2 Windows Server 2008 R2, codenamed "Windows Server 7" or "Windows Server 2008 Release 2", is the eighth major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server brand name. It was release ...

were released to manufacturing (RTM) and released to the public three months later on October 22, 2009. Unlike its predecessor, Windows Vista, which introduced a large number of new features, Windows 7 was intended to be a more focused, incremental upgrade to the Windows line, with the goal of being compatible with applications and hardware with which Windows Vista was already compatible. Windows 7 has

multi-touch In computing, multi-touch is technology that enables a surface (a touchpad or touchscreen) to recognize the presence of more than one somatosensory system, point of contact with the surface at the same time. The origins of multitouch began at CE ...

support, a redesigned

Windows shell The Windows shell is the graphical user interface for the Microsoft Windows operating system. Its readily identifiable elements consist of the desktop, the taskbar, the Start menu, the task switcher and the AutoPlay feature. On some versions of ...

with an updated

with revealable jump lists that contain shortcuts to files frequently used with specific applications and shortcuts to tasks within the application, a home networking system called HomeGroup, and performance improvements.

= Windows 8 and 8.1

Windows 8 Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on August 1, 2012, made available for download via Microsoft ...

, the successor to Windows 7, was released generally on October 26, 2012. A number of significant changes were made on Windows 8, including the introduction of a user interface based around Microsoft's Metro design language with optimizations for touch-based devices such as tablets and all-in-one PCs. These changes include the Start screen, which uses large tiles that are more convenient for touch interactions and allow for the display of continually updated information, and a new class of apps which are designed primarily for use on touch-based devices. The new Windows version required a minimum resolution of 1024×768 pixels, effectively making it unfit for

netbook A netbook is a small-sized laptop computer; they were primarily sold from 2007 until around 2013, designed mostly as a means of accessing the Internet and being significantly less expensive than regular-sized laptops. At their inception in l ...

s with 800×600-pixel screens. Other changes include increased integration with

cloud services Cloud computing is "a paradigm for enabling network access to a scalable and elastic pool of shareable physical or virtual resources with self-service provisioning and administration on-demand," according to ISO. Essential characteristics ...

and other online platforms (such as

social networks A social network is a social structure consisting of a set of social actors (such as individuals or organizations), networks of dyadic ties, and other social interactions between actors. The social network perspective provides a set of meth ...

and Microsoft's own

OneDrive Microsoft OneDrive is a file-hosting service operated by Microsoft. First released as SkyDrive in August 2007, it allows registered users to store, share, back-up and synchronize their files. OneDrive also works as the storage Frontend and backe ...

(formerly SkyDrive) and

Xbox Live The Xbox network, formerly known and commonly referred to as Xbox Live, is an online multiplayer gaming and digital media delivery service created and operated by Microsoft Gaming for the Xbox brand. It was first made available to the origina ...

services), the

Windows Store The Microsoft Store (formerly known as the Windows Store) is a digital distribution platform operated by Microsoft. It was created as an app store for Windows 8 as the primary means of distributing Universal Windows Platform apps. With ...

service for software distribution, and a new variant known as Windows RT for use on devices that utilize the

ARM architecture ARM (stylised in lowercase as arm, formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a family of reduced instruction set computer, RISC instruction set architectures (ISAs) for central processing unit, com ...

, and a new keyboard shortcut for

screenshot A screenshot (also known as screen capture or screen grab) is an analog or digital image that shows the contents of a computer display. A screenshot is created by a (film) camera shooting the screen or the operating system An operating sys ...

s. An update to Windows 8, called Windows 8.1, was released on October 17, 2013, and includes features such as new live tile sizes, deeper

integration, and many other revisions.

and Windows 8.1 have been subject to some criticism, such as the removal of the Start menu.

= Windows 10

On September 30, 2014, Microsoft announced

as the successor to Windows 8.1. It was released on July 29, 2015, and addresses shortcomings in the user interface first introduced with Windows 8. Changes on PC include the return of the Start Menu, a

virtual desktop In computing, a virtual desktop is a term used with respect to user interfaces, usually within the WIMP (computing), WIMP paradigm, to describe ways in which the virtual space of a computer's desktop environment is expanded beyond the physical ...

system, and the ability to run Windows Store apps within windows on the desktop rather than in full-screen mode.

is said to be available to update from qualified

with SP1, Windows 8.1 and Windows Phone 8.1 devices from the Get Windows 10 Application (for

, Windows 8.1) or

Windows Update Windows Update is a Microsoft service for the Windows 9x and Windows NT families of the Microsoft Windows operating system, which automates downloading and installing Microsoft Windows software updates over the Internet. The service delivers sof ...

(

). In February 2017, Microsoft announced the migration of its Windows source code repository from Perforce to

Git Git () is a distributed version control system that tracks versions of files. It is often used to control source code by programmers who are developing software collaboratively. Design goals of Git include speed, data integrity, and suppor ...

. This migration involved 3.5 million separate files in a 300-gigabyte repository. By May 2017, 90 percent of its engineering team was using Git, in about 8500 commits and 1760 Windows builds per day. In June 2021, shortly before Microsoft's announcement of Windows 11, Microsoft updated their lifecycle policy pages for Windows 10, revealing that support for their last release of Windows 10 will end on October 14, 2025. On April 27, 2023, Microsoft announced that version 22H2 would be the last of Windows 10. Windows logo and wordmark - 2021

= Windows 11

= On June 24, 2021,

was announced as the successor to Windows 10 during a livestream. The new operating system was designed to be more user-friendly and understandable. It was released on October 5, 2021. Windows 11 is a free upgrade to Windows 10 users who meet the system requirements.

Windows 365

In July 2021, Microsoft announced it will start selling subscriptions to virtualized Windows desktops as part of a new ''Windows 365'' service in the following month. The new service will allow for cross-platform usage, aiming to make the operating system available for both Apple and Android users. It is a separate service and offers several variations including Windows 365 Frontline, Windows 365 Boot, and the Windows 365 app. The subscription service will be accessible through any

with a

. The new service is an attempt at capitalizing on the growing trend, fostered during the

COVID-19 pandemic The COVID-19 pandemic (also known as the coronavirus pandemic and COVID pandemic), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), began with an disease outbreak, outbreak of COVID-19 in Wuhan, China, in December ...

, for businesses to adopt a hybrid

remote work Remote work (also called telecommuting, telework, work from or at home, WFH as an initialism, hybrid work, and other terms) is the practice of work (human activity), working at or from one's home or Third place, another space rather than from ...

environment, in which "employees split their time between the office and home". As the service will be accessible through web browsers, Microsoft will be able to bypass the need to publish the service through

Google Play Google Play, also known as the Google Play Store, Play Store, or sometimes the Android Store (and was formerly Android Market), is a digital distribution service operated and developed by Google. It serves as the official app store for certifie ...

or the Apple App Store. Microsoft announced Windows 365 availability to business and enterprise customers on August 2, 2021.

Multilingual support

Multilingual support has been built into Windows since Windows 3.0. The language for both the keyboard and the interface can be changed through the Region and Language Control Panel. Components for all supported input languages, such as Input Method Editors, are automatically installed during Windows installation (in Windows XP and earlier, files for East Asian languages, such as Chinese, and files for right-to-left scripts, such as Arabic, may need to be installed separately, also from the said Control Panel). Third-party IMEs may also be installed if a user feels that the provided one is insufficient for their needs. Since Windows 2000, English editions of Windows NT have East Asian IMEs (such as Microsoft Pinyin IME and Microsoft Japanese IME) bundled, but files for East Asian languages may be manually installed on Control Panel. Interface languages for the operating system are free for download, but some languages are limited to certain editions of Windows. Language Interface Packs (LIPs) are redistributable and may be downloaded from Microsoft's Download Center and installed for any edition of Windows (XP or later)they translate most, but not all, of the Windows interface, and require a certain base language (the language which Windows originally shipped with). This is used for most languages in emerging markets. Full Language Packs, which translate the complete operating system, are only available for specific editions of Windows (Ultimate and Enterprise editions of Windows Vista and 7, and all editions of Windows 8, 8.1 and RT except Single Language). They do not require a specific base language and are commonly used for more popular languages such as French or Chinese. These languages cannot be downloaded through the Download Center, but are available as optional updates through the

service (except Windows 8). The interface language of installed applications is not affected by changes in the Windows interface language. The availability of languages depends on the application developers themselves.

and

Windows Server 2012 Windows Server 2012, codenamed "Windows Server 8", is the ninth major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server brand name. It is the server version of Windows based on Windows ...

introduce a new Language Control Panel where both the interface and input languages can be simultaneously changed, and language packs, regardless of type, can be downloaded from a central location. The PC Settings app in Windows 8.1 and Windows Server 2012 R2 also includes a counterpart settings page for this. Changing the interface language also changes the language of preinstalled

apps (such as Mail, Maps and News) and certain other Microsoft-developed apps (such as Remote Desktop). The above limitations for language packs are however still in effect, except that full language packs can be installed for any edition except Single Language, which caters to emerging markets.

Platform support

Windows NT included support for several platforms before the

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

-based

personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...

became dominant in the professional world. Windows NT 4.0 and its predecessors supported

DEC Alpha Alpha (original name Alpha AXP) is a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC). Alpha was designed to replace 32-bit VAX complex instruction set computers ( ...

and MIPS R4000 (although some of the platforms implement

64-bit computing In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit central processing units (CPU) and arithmetic logic units (ALU) are those that are based on processor registers, ...

, the OS treated them as 32-bit). Windows 2000 dropped support for all platforms, except the third generation x86 (known as

IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called ''i386'') is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the i386, 80386 microprocessor in 1985. IA-32 is the first incarn ...

) or newer in 32-bit mode. The client line of the Windows NT family still ran on IA-32 up to

(the server line of the Windows NT family still ran on IA-32 up to

). With the introduction of the Intel Itanium architecture (

IA-64 IA-64 (Intel Itanium architecture) is the instruction set architecture (ISA) of the discontinued Itanium family of 64-bit Intel microprocessors. The basic ISA specification originated at Hewlett-Packard (HP), and was subsequently implemented by ...

), Microsoft released new versions of Windows to support it. Itanium versions of

and

were released at the same time as their mainstream x86 counterparts. Windows XP 64-Bit Edition (Version 2003), released in 2003, is the last Windows client operating system to support Itanium. Windows Server line continues to support this platform until

; Windows Server 2008 R2 is the last Windows operating system to support Itanium architecture. On April 25, 2005, Microsoft released Windows XP Professional x64 Edition and Windows Server 2003 x64 editions to support

x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit extension of the x86 instruction set architecture, instruction set. It was announced in 1999 and first available in the AMD Opteron family in 2003. It introduces two new ope ...

(or simply x64), the 64-bit version of x86 architecture.

was the first client version of Windows NT to be released simultaneously in IA-32 and x64 editions. As of 2024, x64 is still supported. An edition of Windows 8 known as Windows RT was specifically created for computers with

, and while ARM is still used for Windows smartphones with Windows 10, tablets with Windows RT will not be updated. Starting from Windows 10 Fall Creators Update (version 1709) and later includes support for ARM-based PCs.

Windows CE

Windows CE (officially known as ''Windows Embedded Compact''), is an edition of Windows that runs on minimalistic computers, like satellite navigation systems and some mobile phones. Windows Embedded Compact is based on its own dedicated kernel, dubbed Windows CE kernel. Microsoft licenses Windows CE to OEMs and device makers. The OEMs and device makers can modify and create their own user interfaces and experiences, while Windows CE provides the technical foundation to do so. Windows CE was used in the

Dreamcast The is the final home video game console manufactured by Sega. It was released in Japan on November 27, 1998, in North America on September 9, 1999 and in Europe on October 14, 1999. It was the first sixth-generation video game console, prec ...

along with Sega's own proprietary OS for the console. Windows CE was the core from which

was derived. Its successor, Windows Phone 7, was based on components from both Windows CE 6.0 R3 and Windows CE 7.0.

however, is based on the same NT-kernel as Windows 8. Windows Embedded Compact is not to be confused with Windows XP Embedded or Windows NT 4.0 Embedded, modular editions of Windows based on Windows NT kernel.

Xbox OS

Xbox OS is an unofficial name given to the version of Windows that runs on

Xbox Xbox is a video gaming brand that consists of four main home video game console lines, as well as application software, applications (games), the streaming media, streaming service Xbox Cloud Gaming, and online services such as the Xbox networ ...

consoles. From

Xbox One The Xbox One is a home video game console developed by Microsoft. Announced in May 2013, it is the successor to Xbox 360 and the third console in the Xbox#Consoles, Xbox series. It was first released in North America, parts of Europe, Austra ...

onwards it is an implementation with an emphasis on virtualization (using Hyper-V) as it is three operating systems running at once, consisting of the core

, a second implemented for games and a more Windows-like environment for applications. Microsoft updates Xbox One's OS every month, and these updates can be downloaded from the Xbox Live service to the Xbox and subsequently installed, or by using offline recovery images downloaded via a PC. It was originally based on NT 6.2 (Windows 8) kernel, and the latest version runs on an NT 10.0 base. This system is sometimes referred to as "Windows 10 on Xbox One". Xbox One and Xbox Series operating systems also allow limited (due to licensing restrictions and testing resources) backward compatibility with previous generation hardware, and the Xbox 360's system is backwards compatible with the original Xbox.

Version control system

Up to and including every version before

, Microsoft used an in-house version control system named Source Library Manager (SLM). Shortly after Windows 2000 was released, Microsoft switched to a fork of Perforce named Source Depot. This system was used up until 2017 once the system could not keep up with the size of Windows. Microsoft had begun to integrate Git into

Team Foundation Server Azure DevOps Server, formerly known as Team Foundation Server (TFS) and Visual Studio Team System (VSTS), is a Microsoft product that provides version control (either with Team Foundation Version Control (TFVC) or Git), reporting, requirements ...

in 2013, but Windows (and Office) continued to rely on Source Depot. The Windows code was divided among 65 different repositories with a kind of virtualization layer to produce unified view of all of the code. In 2017 Microsoft announced that it would start using

, an open source version control system created by

Linus Torvalds Linus Benedict Torvalds ( , ; born 28 December 1969) is a Finnish software engineer who is the creator and lead developer of the Linux kernel. He also created the distributed version control system Git. He was honored, along with Shinya Yam ...

, and in May 2017 they reported that the migration into a new Git repository was complete.

VFSForGit

Each Git repository contains a complete history of all the files, which tends to be very large for Windows. Microsoft has been working on a new project called the Virtual File System for Git (VFSForGit) to address these challenges. In 2021 the VFS for Git was superseded by Scalar.

Timeline of releases

Usage share and device sales

Use of

has exceeded Windows 7 globally since early 2018. For desktop and laptop computers, according to Net Applications and StatCounter (which track the use of operating systems in devices that are active on the Web), Windows was the most used operating-system family in August 2021, with around 91% usage share according to Net Applications and around 76% usage share according to StatCounter. Including personal computers of all kinds (e.g., desktops, laptops, mobile devices, and game consoles), Windows OSes accounted for 32.67% of usage share in August 2021, compared to Android (highest, at 46.03%),

iOS Ios, Io or Nio (, ; ; locally Nios, Νιός) is a Greek island in the Cyclades group in the Aegean Sea. Ios is a hilly island with cliffs down to the sea on most sides. It is situated halfway between Naxos and Santorini. It is about long an ...

's 13.76%,

's 2.81%, and macOS's 2.51%, according to Net Applications and 30.73% of usage share in August 2021, compared to Android (highest, at 42.56%), iOS/iPadOS's 16.53%, and macOS's 6.51%, according to StatCounter. Those statistics do not include servers (including

cloud computing Cloud computing is "a paradigm for enabling network access to a scalable and elastic pool of shareable physical or virtual resources with self-service provisioning and administration on-demand," according to International Organization for ...

, where Linux has significantly more market share than Windows) as Net Applications and StatCounter use web browsing as a proxy for all use.

Security

Early versions of Windows were designed at a time where

malware Malware (a portmanteau of ''malicious software'')Tahir, R. (2018)A study on malware and malware detection techniques . ''International Journal of Education and Management Engineering'', ''8''(2), 20. is any software intentionally designed to caus ...

and networking were less common, and had few built-in security features; they did not provide access privileges to allow a user to prevent other users from accessing their files, and they did not provide

memory protection Memory protection is a way to control memory access rights on a computer, and is a part of most modern instruction set architectures and operating systems. The main purpose of memory protection is to prevent a process from accessing memory that h ...

to prevent one process from reading or writing another process's address space or to prevent a process from code or data used by privileged-mode code. While the

series offered the option of having profiles for multiple users with separate profiles and home folders, it had no concept of access privileges, allowing any user to edit others' files. In addition, while it ran separate 32-bit applications in separate address spaces, protecting an application's code and data from being read or written by another application, it did not protect the first megabyte of memory from userland applications for compatibility reasons. This area of memory contains code critical to the functioning of the operating system, and by writing into this area of memory an application can crash or freeze the operating system. This was a source of instability as faulty applications could accidentally write into this region, potentially corrupting important operating system memory, which usually resulted in some form of system error and halt.

was far more secure, implementing access privileges and full memory protection, and, while 32-bit programs meeting the DoD's C2 security rating, yet these advantages were nullified by the fact that, prior to

, the default user account created during the setup process was an administrator account; the user, and any program the user launched, had full access to the machine. Though

did offer an option of turning administrator accounts into limited accounts, the majority of home users did not do so, partially due to the number of programs which required administrator rights to function properly. As a result, most home users still ran as administrator all the time. These architectural flaws, combined with Windows's very high popularity, made Windows a frequent target of

computer worm A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers. It often uses a computer network to spread itself, relying on security failures on the target computer to access it. It will ...

and

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

writers. Furthermore, although Windows NT and its successors are designed for security (including on a network) and multi-user PCs, they were not initially designed with Internet security in mind as much, since, when it was first developed in the early 1990s, Internet use was less prevalent. In a 2002 strategy memo entitled "Trustworthy computing" sent to every Microsoft employee, Bill Gates declared that security should become Microsoft's highest priority.

introduced a privilege elevation system called User Account Control. When logging in as a standard user, a logon session is created and a token containing only the most basic privileges is assigned. In this way, the new logon session is incapable of making changes that would affect the entire system. When logging in as a user in the Administrators group, two separate tokens are assigned. The first token contains all privileges typically awarded to an administrator, and the second is a restricted token similar to what a standard user would receive. User applications, including the

, are then started with the restricted token, resulting in a reduced privilege environment even under an Administrator account. When an application requests higher privileges or "Run as administrator" is clicked, UAC will prompt for confirmation and, if consent is given (including administrator credentials if the account requesting the elevation is not a member of the administrators group), start the process using the unrestricted token. Leaked documents from 2013 to 2016 codenamed Vault 7 detail the capabilities of the CIA to perform electronic surveillance and cyber warfare, such as the ability to compromise operating systems such as Windows. In August 2019, computer experts reported that the BlueKeep security vulnerability, , that potentially affects older unpatched Windows versions via the program's Remote Desktop Protocol, allowing for the possibility of remote code execution, may include related flaws, collectively named '' DejaBlue'', affecting newer Windows versions (i.e.,

and all recent versions) as well. In addition, experts reported a Microsoft security vulnerability, , based on

legacy code Legacy or Legacies may refer to: Arts and entertainment Comics * " Batman: Legacy", a 1996 Batman storyline * '' DC Universe: Legacies'', a comic book series from DC Comics * ''Legacy'', a 1999 quarterly series from Antarctic Press * ''Legacy ...

involving Microsoft CTF and ctfmon (ctfmon.exe), that affects all

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

versions from

to the then most recent

versions; a patch to correct the flaw is available. Microsoft releases security patches through its

service approximately once a month (usually the second Tuesday of the month), although critical updates are made available at shorter intervals when necessary. Versions subsequent to Windows 2000 SP3 and Windows XP implemented automatic download and installation of updates, substantially increasing the number of users installing security updates. Windows integrates the Windows Defender antivirus, which is seen as one of the best available. Windows also implements Secure Boot, Control Flow Guard, ransomware protection,

BitLocker BitLocker is a full volume encryption feature included with Microsoft Windows versions starting with Windows Vista. It is designed to protect data by providing encryption for entire volumes. By default, it uses the Advanced Encryption Standard ...

disk encryption, a firewall, and Windows SmartScreen. In July 2024, Microsoft signalled an intention to limit kernel access and improve overall security, following a highly publicised CrowdStrike update that caused 8.5 million Windows PCs to crash. Part of that initiative is to rewrite parts of Windows in

Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

, a memory-safe language.

File permissions

All Windows versions from Windows NT 3 have been based on a file system permission system referred to as AGDLP (Accounts, Global, Domain Local, Permissions) in which file permissions are applied to the file/folder in the form of a 'local group' which then has other 'global groups' as members. These global groups then hold other groups or users depending on different Windows versions used. This system varies from other vendor products such as

and

due to the 'static' allocation of permission being applied directly to the file or folder. However using this process of AGLP/AGDLP/AGUDLP allows a small number of static permissions to be applied and allows for easy changes to the account groups without reapplying the file permissions on the files and folders.

Alternative implementations

Owing to the operating system's popularity, a number of applications have been released that aim to provide compatibility with Windows applications, either as a

compatibility layer In software engineering, a compatibility layer is an interface that allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system calls for the host system. With s ...

for another operating system, or as a standalone system that can run software written for Windows out of the box. These include: *

Wine Wine is an alcoholic drink made from Fermentation in winemaking, fermented fruit. Yeast in winemaking, Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made f ...

– a

free and open-source Free and open-source software (FOSS) is software available under a Software license, license that grants users the right to use, modify, and distribute the software modified or not to everyone free of charge. FOSS is an inclusive umbrella term ...

implementation of the

, allowing one to run many Windows applications on x86-based platforms, including

UNIX Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

and

. Wine developers refer to it as a "compatibility layer" and use Windows-style APIs to emulate Windows environment. ** CrossOver – a Wine package with licensed fonts. Its developers are regular contributors to Wine. **

Proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

– A fork of Wine by Valve to run Windows games on Linux and other Unix-like OS. *

ReactOS ReactOS is a Free and open-source software, free and open-source operating system for i586/amd64 personal computers that is intended to be binary-code compatibility, binary-compatible with computer programs and device drivers developed for Wind ...

– an open-source OS intended to run the same software as Windows, originally designed to simulate Windows NT 4.0, later aiming at Windows 7 compatibility. It has been in the development stage since 1996. *Freedows OS – an open-source attempt at creating a Windows clone for x86 platforms, intended to be released under the

GNU General Public License The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

. Started in 1996 by Reece K. Sellin, the project was never completed, getting only to the stage of design discussions which featured a number of novel concepts until it was suspended in 2002.

References

Operating system families Products introduced in 1985 1985 establishments in the United States