Microsoft Windows

Microsoft Windows, commonly referred to as Windows, is a family of proprietary graphical operating systems developed by Microsoft, which includes various products for different markets and industries that use a similar user interface and feature set. The original version of Windows was an operating environment that ran on top of MS-DOS, although later versions increasingly took on the characteristics of a full operating system. Since Windows XP, all desktop versions of Windows use the portable NT hybrid kernel that does not rely on MS-DOS.

The Windows family currently encompasses the main consumer version named simply Windows, as well as Windows Server for the server market and Windows IoT for the embedded market, although they are all based on the common desktop Windows codebase. Internally, another variant called Windows Core OS is also currently in development, which is also based on the NT kernel, although it is not based on desktop Windows. In the past, the family also included Windows RT for ARM-based tablets, Windows Phone and Windows Mobile for smartphones, Windows Embedded Compact, or the MS-DOS based line.

Since Windows 95, most Windows versions have used the same user interface that included the Start menu, a taskbar on the edge of the screen and a desktop, as well as overlapping or full screen windows with controls in their top right.

16-bit Windows
Microsoft Windows debuted to the world during the Fall COMDEX 1983 computer expo as a cooperative multitasking desktop environment with a tiling window manager. Contrary to popular belief, the tiling was not a design nor legal limitation, but rather a conscious choice for main application windows backed by research at Xerox PARC, where some members of the Windows team previously worked at. Windows did indeed also support overlapping windows, although in the ability was originally only used for popup windows and certain controls such as menus and dropdowns. Although Windows ended up supporting MS-DOS hosts only until the introduction of NT, Microsoft also considered porting Windows to Xenix as well as the multitasking MS-DOS 4. However, neither port ended up materializing.

After multiple delays in its development, Windows 1.0 finally hit the market on 20 November 1985 and achieved modest success, with over 500 thousand copies sold during its shelf life. Several minor updates were released in the following years, adding support for more hardware and languages. The first version used the MS-DOS Executive, a simple file manager, as a shell, which is generally the first application ran on startup providing the user experience. Other applications included in the package Calculator, Cardfile, Clipboard Viewer, Clock, Control Panel, Notepad, Paint, Reversi, Spooler, Terminal, and Write.

A major update called Windows 2.0 was released in 1987 adding features such as universally overlapping windows, which later lead to Apple filing a lawsuit for copyright infringement. This version also introduced general support for VGA and PS/2 mouse (later OEM versions of Windows 1.0 already included it). A separate edition called Windows/386 was also introduced that took advantage of the virtual 8086 mode of the i386 processor to preemptively multitask MS-DOS applications under Windows; this would be later known as the 386 Enhanced Mode and become the cornerstone of Windows 9x. In later revisions of the Windows 2.0 series, the original edition was renamed Windows/286.

Windows 3.0 was released in 1990 and became the first widely successful version of Windows. The new features included a revamped user experience consisting of the Program Manager, which allowed easy management of installed applications. A new File Manager was also included to replace the former shell, which was now deprecated. The previously separate 286 and 386 editions of Windows were unified into one version with the ability to operate in three different modes according to the hardware configuration:
 * Real mode, which was intended for computers with the original 8088/8086 processor. This was also the only mode which fully supported applications written for earlier versions of Windows.
 * Standard mode, which used the protected mode feature of the 286 and 386 processors in order to gain access to memory beyond the first 640K, although it still switched to real mode to run MS-DOS applications.
 * 386 Enhanced mode, which in addition to the protected mode also used the 386 processor's ability to create and manage virtual machines for real mode MS-DOS applications.

A major update dubbed Windows 3.1 followed in 1992, introducing the new flag logo with colored panes. The user interface was refreshed in this release, including new, more vivid icons. This version of Windows removed support for real mode and the MS-DOS Executive application. It was accompanied by Windows for Workgroups 3.1 with integrated networking support. An add-on pack named Win32s was also introduced in 1992, which allowed Windows 3.1 users to run simpler 32-bit Windows applications in the otherwise 16-bit environment and provided early testing for a more complete Win32 implementation in the next major version of DOS-based Windows.

The last minor update to the series, Windows for Workgroups 3.11 was released in 1993 and introduced 32-bit disk access as well as removed the Standard mode, raising the minimum required CPU to a 386. A 32-bit TCP/IP stack was ported from an early version of Windows 95 and released in 1994 as a downloadable plugin for Windows for Workgroups 3.11.

Windows NT
In 1988, Microsoft hired Dave Cutler, a former DEC engineer, to create a portable 32-bit version of OS/2, the operating system that the company worked on in collaboration with IBM. At the time, OS/2 was a 16-bit operating system very much tied to the x86 platform with considerable DOS heritage. The new operating system intended to be a preemptive multitasking system with multiprocessing support. The design included a portable kernel with executive services layered on top of a hardware abstraction layer, and multiple environmental subsystems running in user mode offering support for multiple APIs. Portable OS/2, or NT OS/2, would have included support for both 16-bit and extended 32-bit variant of the OS/2 API, as well as virtual DOS machines and an implementation of the POSIX standard, which would allow Microsoft to run for US government contracts. Commercial release was planned for the early 1990s with NT shipping as OS/2 3.0, while IBM was adding 32-bit support to the original OS/2 codebase to create OS/2 2.0.

Initially, NT was developed for the Intel i860 processor, partially to ensure portability by preventing programmers from introducing x86-specific paradigms into code. When the team learned about the disappointing performance of the i860, the operating system was ported to the i386 and MIPS architectures.

Following the success of Windows 3.0 in 1990, Microsoft revised its OS/2 plans as a part of its new "Windows Everywhere" strategy, which tried to position Windows as a common environment that could run the same apps on DOS and OS/2 as well as on the new NT platform. This included the addition of a Windows subsystem to OS/2 3.0 as a peer to the existing OS/2 environment. However, this didn't improve the already deteriorating Microsoft-IBM relationship and led eventually to its collapse. The design of NT was then further changed as the Windows became the main environment providing the system's user interface, while OS/2 support was reduced to character mode OS/2 1.x applications. The change was first announced in January 1991 with the new operating system initially being called Advanced Windows.

User interface was added to Windows NT in the first half of 1991, with network support following during summer. The first prototype version was shipped to selected partners in September and the new operating system was publicly demonstrated for the first time at Fall COMDEX 1991 in October. A MIPS build first shipped in a December release. Later builds added crucial components such as the registry, NTFS and the ability to run 16-bit MS-DOS and Windows applications. Windows NT 3.1 was finally released on 27 October 1993 in workstation and server flavors.

DEC filed a lawsuit during NT development, alleging that Microsoft used stolen code from the DEC MICA operating system. The case was settled out of court, with Microsoft adding support for the DEC Alpha processor in an updated version of Windows NT 3.1.

The next minor version, Windows NT 3.5 was released in 1994 and included performance improvement as well as a new full TCP/IP stack, long filename (LFN) support on the FAT file system and other refinements. Windows NT 3.51 was released in 1995, which ensured compatibility with the upcoming Windows 95 and added support for the PowerPC architecture, the PCMCIA interface, as well as file compression, or replaceable GINA.

Windows 9x
Microsoft first announced a 32-bit version of Windows that would run on top of MS-DOS in 1991. Several plans for a low-end Win32 environment were considered, including a variant of the NT kernel cut down in order to run on an average Windows 3.1 computer. In the end, Microsoft decided to build the new version on top of MS-DOS and Windows in 386 Enhanced mode.

On 24 August 1995, Microsoft released Windows 95, previously known under its codename "Chicago", with a brand new user interface with a Start menu, taskbar, and the desktop, as provided by the new Windows Explorer. Although previous versions already included certain 32-bit components, it was the first version to be able to run most 32-bit user applications, while it kept a great degree of compatibility with already existing 16-bit ones. Among other improvements in this version was the support for long filenames through an extension to the FAT16 file system.

Windows 95 was the first widespread release of Windows to be integrated with a specific MS-DOS version, although Windows 3.1 was also available before in combined packages with MS-DOS 5 and later MS-DOS 6, which were based on the Janus project. However, MS-DOS 7 in Windows 95 was used only as a bootloader and a compatibility layer for ancient device drivers. Most MS-DOS user applications were either extended with Windows code or entirely replaced with a Windows version, keeping only the ones that were required to run without Windows, e.g. during the OS installation, such as  and.

The new user interface was also ported to the Windows NT line, with several Shell Technology Previews being released for Windows NT 3.51 during the development of Chicago and the Shell Update Release shipping in 1996 as Windows NT 4.0. Alongside the new shell, Windows NT 4.0 also notably moved a part of the GUI stack into kernel mode, which greatly improved performance.

During its lifetime Windows 95 saw several larger updates dubbed the OEM Service Releases (OSR) that were released only to computer manufacturers, specifically OSR 1.0, OSR 2.0, OSR 2.1, and OSR 2.5. A Service Pack was also released that updated an RTM copy of Windows 95 to the OSR 1.0 level. In 1997 a USB Supplement was released for OSR 2.x that added support for the then-new Universal Serial Bus interface.

The classic Windows line received a major update on 25 June 1998 with the release of Windows 98, codenamed "Memphis". It was the first version to integrate Internet Explorer deeply into the operating system's user interface as a part of the Windows Desktop Update. Many parts of the UI started using HTML and Internet Explorer's rendering engine to present a web-like user interface. A feature called Active Desktop made it even possible to set a webpage as the desktop background. Under the hood Windows 98 introduced the new Windows Driver Model, which enabled the use of the same drivers on Windows 9x as well as on the radically different Windows NT based operating systems.

A year later, Windows 98 received an update which was called the Second Edition, which included a new version of Internet Explorer, added Internet Connection Sharing and improved USB support.

In 2000, Windows Me (Millennium Edition), the last release of the classic Windows line was released. It carried over the improvements made to the user interface in its NT-based counterpart, Windows 2000. Windows Me is based on Windows 98, however, access to the real mode MS-DOS was restricted in order to decrease boot time among other changes to the kernel. It was infamously known for its stability problems partially caused by the rushing of its release following the cancelation of the Neptune project. It was replaced by Windows XP in 2001, ending the era of classic Windows.

Windows 2000 and Windows XP
In the late 1990s it became more feasible to discontinue the aging Windows 9x line and release a consumer version based on Windows NT. Microsoft started work on the the next version of Windows NT immediately after the release of Windows NT 4.0, which would improve the user experience of the high-end operating system. Similar to Memphis, the user interface of Windows NT 5.0 initially used Internet Explorer 4.0 with the Windows Desktop Update, being later updated to 5.0 and then 5.5 during development. Management tools, most of which were left unchanged since the first NT release, were rewritten using the new Microsoft Management Console. On servers, the new version brought improvements from the canceled Cairo project, such as Active Directory.

Beside working on the successor of Windows NT 4.0, Microsoft also released several new editions based on the NT 4.0 codebase. An Enterprise edition of Windows NT 4.0 Server was released in 1997, which was the predecessor of the Advanced Server SKU of later versions and was intended for high traffic and high demand workloads. Terminal Server Edition followed in 1998, which introduced the Terminal Services feature, allowing remote access to Windows computers. Windows NT Embedded 4.0 was introduced in 1999, a specialized version of the Workstation edition that allowed embedded vendors to pick only the required OS components for the intended workloads.

As Windows NT 5.0 got further delayed, the consumer NT aspect was moved into a following release codenamed Neptune, which would succeed Windows 98 and later Windows Me. In 1998, Microsoft announced that Windows NT 5.0 would be called Windows 2000, dropping the NT moniker to mark the NT technology becoming mainstream. In the end, it was released on 17 February 2000 with Internet Explorer 5.5 and earned the reputation as one of the most stable versions of Windows.

Work on Neptune begun several months before Windows 2000 was finished. The Neptune team heavily cooperated with the team working on Millennium, with the two projects sharing certain components. Development concentrated on a new task-oriented user interface called Activity Centers, which was also included in contemporary Millennium builds. The project also toyed around with the idea of hybrid startup, later implemented in Windows 8. Neptune was canceled in early 2000 together with its business counterpart codenamed Odyssey and replaced with a new, more conservative project codenamed Whistler that would eventually become Windows XP.

Windows XP was released on 25 October 2001 and was a relatively minor update to Windows 2000, mostly focusing on user experience and better compatibility with Windows 9x. A new theme called Luna was introduced, replacing the classic theme used in previous versions. A new login screen and fast user switching was also added, as well as better support for digital cameras, MS-DOS emulation and wireless networking. Windows XP was originally released in Home Edition and Professional variants, with an embedded version following a few months after. The 64-Bit Edition was also originally launched for the Itanium (IA-64) architecture.

Two additional editions for consumer use were introduced in 2002, both based on the original Professional edition. Windows XP Media Center Edition added the Windows Media Center (and later the Royale theme), while Windows XP Tablet PC Edition added tools and games for use on a Microsoft Tablet PC.

Development of the server counterpart continued after the release of the client version, resulting in Windows Server 2003, which was released in spring 2003 and used a newer kernel. It was also the base for an updated version of the Windows XP 64-Bit Edition. Work on an AMD64 version started late in the development process and finished in 2005 with the release of x64 editions of both Windows Server 2003 and Windows XP Professional (also based on 2003 codebase).

The Windows XP Starter Edition was introduced in 2004 for developing markets, including various Asian and South American countries and Russia. It is based on the original Home Edition, but is noticeably more limited with some features removed and only 3 programs being allowed to run at a time.

In 2005, Microsoft was forced to introduce a version of Windows XP without the Windows Media Player to the European market after the European Commission ruled that the company had been breaking its near monopoly in the operating systems market by including the player. The company therefore came up with a new edition originally called Windows XP Reduced Media Edition that didn't include the Media Player as well as Windows Media Player, although allowing the user to download them for free from Microsoft's website. However, the European authorities objected to the name and instead suggested the N suffix for both Home Edition and Professional, standing for "not with Media Player". The N editions were available for the same price as the regular variants, which lead to low consumer demand and some OEMs not offering it at all. The K and KN editions have been introduced in 2006 after a similar ruling by South Korean authorities, with the K edition adding links to third party media player and instant messaging software, and the KN edition in addition removing the Windows Media Player and Windows Messenger.

Windows Vista and Windows 7
Work on a new, major release of Windows started already before Whistler concluded development. The project, codenamed Blackcomb as a reference to the Whistler Blackcomb ski resort in British Columbia, was originally announced as the successor of Windows XP with new features such as a .NET user interface, integration with web services, or an advanced storage subsystem. However, the company realized that it wouldn't be able to hit the expected release date of late 2002 with the planned feature set and decided to first ship a bridge-gap release known as Longhorn, named after a bar between the two mountains, followed by Blackcomb itself in 2003 or 2004.

Development of Longhorn started in 2002, initially as a spinoff of the still-ongoing server version of Windows XP. At the time, Longhorn work was mostly confined to, the lab that worked on the Windows shell and user experience. As Windows Server 2003 finished development, Longhorn development fully took off as new features such as Avalon or WinFS were added. With the cancellation of Longhorn Server in late 2002, most user experience features were moved to Longhorn while server-oriented improvements were slated for Blackcomb.

As development progressed, many features originally planned for Blackcomb became part of Longhorn, causing both projects to be postponed even further. The project was subject to severe feature creep, as well as organizational issues. Many components were extended using the .NET Framework and Managed Extensions for C++, both still relatively new technologies at the time, which lead to increasing stability issues. Most builds were plagued with memory leaks, resulting in only two semi-public releases during this period. Managed Extensions for C++ were later deprecated and replaced with C++/CLI as a direct result of the negative experience from its usage in Longhorn.

In the end, the Longhorn project was reset in the middle of 2004. The feature set was reviewed and many features such as WinFS or Castles were postponed or canceled in order to create a more realistic set of goals for the new major version. The remaining features were reimplemented in C/C++ as a ban on .NET code was introduced, with the exception of Windows Media Center. The first build of Longhorn after the reset was released to WinHEC 2005 attendees in the spring of 2005, followed by the first beta release three months later, which introduced the Windows Vista name.

The development continued at a steady pace, with Beta 2 shipping in May 2006 and two release candidates following in the months after. Windows Vista was finally released on 30 January 2007 in considerably more editions than its predecessor, which included Starter, Home Basic, Home Premium, Business, Ultimate and Enterprise. The new version included a new overhauled user interface called Windows Aero, as well as new security features such as User Account Control. It grew on to become one of the most disliked releases of Windows due to its immense lack of stability of the original release, although later updates greatly improved the situation. The large jump in system requirements caused by the long gap since the last Windows release and computer manufacturers marking underperforming systems as Vista Capable also contributed to its bad reputation. The server counterpart, Windows Server 2008 was released a year later on 27 February 2008 and is based on Windows Vista Service Pack 1.

As Windows Vista was nearing completion in early 2006, the Blackcomb project was renamed to Vienna. However, so many features have been postponed into it after the development reset in 2004 that its objectives became very unrealistic, which lead to its eventual cancelation. A new project codenamed Windows 7 was set up in its place, which aimed to make minor improvements to the core Windows Vista experience such as the introducing the Superbar, Libraries or Homegroups and address the negative feedback its predecessor faced. It was released on 22 October 2009 together with Windows Server 2008 R2 and became one of the most popular versions, with as much as 20% of all Windows users still using it as of 2021.

Windows 8
The popularity of devices utilizing touch input grew significantly during the late 2000s, and while Windows tried to cater to these audiences with the introduction of the Windows XP Tablet PC Edition and later the integration of its features into regular editions of following Windows versions, the Microsoft Tablet PC concept was ultimately rendered obsolete with the introduction of the original iPad in 2010. Unlike the Tablet PC, which usually was an x86-based laptop with a touch screen and software optimized for use with a stylus, the iPad was ARM-based, didn't include a hardware keyboard and used software optimized for finger touch. This led Microsoft to work on a new version of Windows that would be better suited for iPad-like devices.

Work on an ARM port of Windows, internally called Windows on ARM or WOA, also started soon after Windows 7 was finished. The core system together with simple apps were able to run on an Asus P835 smartphone as soon as January 2010. The new port was announced at the 2011 Consumer Electronics Show in January 2011, with the full Windows desktop shown running on boards using nVidia and Texas Instruments system-on-chip circuits.

A new user interface based on the Metro design language was also introduced alongside the Windows Runtime, an application platform used for new, Modern apps designed for it. The new interface, often referred to as Metro, was designed from the ground up with touch input in mind -- the new Modern apps ran in full screen and a second app could be snapped to a side with a large enough screen, allowing for up to two apps to be visible at any time. The Start menu was redesigned as a full screen interface with differently sized tiles, some of which could also display certain information using a feature known as Live Tiles. It also made great use of touch and mouse gestures, to the point that the Start button was replaced by such a gesture. An almost finished version of Metro was first demonstrated in June 2011 at the D9 All Things Digital conference.

Prior to the official announcement of Windows 8, the new features in its pre-release builds were infamously locked down using Redpill, which made it notoriously difficult to research these features even after release. The Developer Preview released during the Microsoft Build 2011 conference in August 2011 is one of the last known builds that still contain the mechanism, although it was already unlocked prior to its distribution. Two more public previews as well as multiple private previews followed in the upcoming months. Windows 8 was finally released on 26 October 2012 alongside Windows Server 2012, and aside from the new Metro interface and ARM port (released as Windows RT), it also included a redesigned File Explorer or Windows To Go, as well as general performance improvements.

Although Metro was generally well received as a tablet user experience, Windows 8 overall was criticized as being way too optimized for touch input to the point of considerably worsening the experience for the majority of Windows users, who use a mouse and a keyboard. A sore point of Metro was its integration with the traditional desktop -- or the lack thereof, as it did not attempt to integrate with the traditional desktop, which was instead treated as yet another app. Overall, the desktop was considered an obsolete platform by Microsoft, as barely any new desktop APIs have been introduced. This went as far as artificially limiting Windows RT to only run Modern applications and Microsoft-signed desktop applications, which ultimately contributed to its market failure.

Windows 8.1, a minor update for Windows 8, was released in October 2013. It addressed some of the general Windows 8 nuisances by restoring the Start button on the taskbar, or adding the ability to boot to the desktop upon logging in. The Metro interface was also improved with updates to the Start screen, which now supported more tile sizes and was more customizable, improved snap view functionality which now allowed more than two apps to be snapped together, or a new unified Search experience based on Bing.

Windows 10 and Windows 11
Development of Windows 10 started after the release of Windows 8.1 in late 2013. The goal was to create a single unified platform that would run on desktop and laptop computers, tablets, smartphones, all-in-one devices and the Xbox and to create a unified application development platform that would also allow apps to run on all Windows 10 based devices. It also aimed to make major improvements to the user interface of the operating system that were criticized in Windows 8.x like bringing back the Start menu, putting the desktop back at center focus and more.

Microsoft also made major changes to how Windows was built and tested by introducing the Windows Insider Program which boosted the company's engagement with beta testers as well as distributing new pre-release builds more frequently than the prior beta testing initiatives. This also greatly cut down the number of leaks from within the company, which in the past bothered the company due to legal complications of licensed features becoming available earlier than expected.

Windows 10 also introduced a new release model called Windows as a service. This allowed new features and improvements to added more frequently to the OS without the need to release a whole new version of Windows every few years.

Development of Windows 11 started in late 2020 and unlike previous versions of Windows, a lot of the work on Windows 11 was isolated in separate development branches and it introduced major overhauls to the user interface to make the operating system easier to use. With Windows 11, Microsoft shifted the operating system to an annual release schedule as opposed to releasing feature updates every 6 months.

Look and feel
Windows allowed customization of its user interface since its first versions. Windows 1.0 and Windows 2.x allowed the user to change the color scheme in their Control Panel, however, there was no selection of pre-made color schemes and the user could only reset to the default scheme by manually editing.

This was improved with Windows 3.0 and its new Colors control panel, which added several color schemes for the user to choose from. Windows NT 3.1 and Windows NT 3.5x also featured the same customization options, although compared to 16-bit Windows where the default preset was provided by the video driver, the defaults were device independent on the new operating system.

Windows 95 introduced a new 3D look inspired by NeXTSTEP and initially only made use of solid colors. This was subsequently refined in Windows 98 and Windows 2000 with the possibility to use 2-color gradients for the titlebar.

Windows XP added support for visual styles, sets of bitmaps that allowed deeper customization of user interface elements. The original release of Windows XP shipped with Luna, while later releases also included Royale. However, users could still switch to Windows Classic if they so chose, which was necessary for accessibility functions such as the High Contrast themes that relied on the classic theme's ability to set individual colors.

Windows Vista introduced the hardware-accelerated Desktop Window Manager, which allowed for advanced effects such as translucent title bars used by the new Windows Aero theme. For users whose hardware were not capable of handling the effects produced by the Aero theme, the software rendered Windows Basic theme was additionally provided within the operating system for lighter footprints.

The option to disable DWM was removed in Windows 8, together with the ability to switch to the Classic theme. The Aero Lite theme was introduced in Windows 8 to replace the classic theme, allowing the user to customize its colors to a greater extent than regular visual styles and providing interoperability with the High Contrast accessibility feature. However, the classic theme implementation as well as support for disabled DWM still remains included with Windows for compatibility purposes.

Supported platforms
Since its initial release, Windows has supported numerous platforms and systems. The original DOS-based line was constrained to systems based on the 8086 processor and later its successors, most important of which was the IBM PC and its successors, including their clones. However, several IBM-incompatible platforms were also supported, notably the Japanese NEC PC-98 architecture.

With the introduction of the portable Windows NT line, support for other processor designs was added. At its peak, Windows NT 4.0 supported x86 as well as MIPS, DEC Alpha and PowerPC. However, the alternative platforms suffered from poor hardware support as well as lack of available software, which lead to the discontinuation of all platforms but x86 in Windows 2000. Windows XP then added support for the newly introduced Itanium, a 64-bit processor designed by Intel purported to eventually replace the aging x86 family. However, its performance proved to be underwhelming and AMD introduced its own 64-bit processor design which was based on the x86, support for which was added in Windows Server 2003 Service Pack 1 and Windows XP Professional x64 Edition.

During the development of Longhorn, Microsoft was experimenting with an ARM port, although it was later scrapped. The idea was revived for Windows 8 in order to target cheap, low power devices. The version of Windows 8 for ARM devices was called Windows RT, and while it was a full Windows environment, it was artificially limited to only run Windows Store applications and Microsoft-signed desktop applications, which contributed to its market failure. ARM64 support was later added to Windows 10, which does not suffer from similar limitations, although the majority of sold Windows 10 devices are still x86-based. ARM64-based Windows has only been made available on devices with Qualcomm SoC's because of a previously exclusivity deal with Qualcomm. With Windows 11, Microsoft dropped support for the 32-bit x86 platform as well as the legacy BIOS boot process, leaving only AMD64 and ARM64 both using UEFI.

Source code
In 2004, incomplete copies of the source code of Windows NT 4.0 and Windows 2000 leaked to the Internet. These leaks were illegal, as the Windows source code is both a trade secret and copyrighted, and as so is protected by law. However, Microsoft has released parts of the source of the Windows Server 2003 kernel for research purposes.

In 2017, The Register and other technology journals reported about a leak of the Windows 10 Shared Source Kits, which are available to qualified customers, enterprises, governments, and partners for debugging and reference purposes, to BetaArchive. Following the controversy, BetaArchive removed all source code content from its archives, which also included the aforementioned incomplete copies of the Windows source code, and adopted a policy of not accepting any more source code material.

In 2018, the source code of the Windows NT File Manager was released on GitHub under the open source MIT license. This was later followed in 2019 by the Windows 10 Calculator application and the console host component.

In May 2020, a copy of the source code of Windows NT 3.5 build 782.1 leaked to the 4chan /vp/ board. Though it can be compiled for the most part, it lacks source files for some components such as encryption. Another leak later followed in September with the source code of Windows XP Service Pack 1 and Windows Server 2003. The leaked copy is mostly complete, although the activation components are absent within both repositories. It is likely that the leak originated from a Microsoft partner who had access to the source code rather than Microsoft itself. This code base had been apparently circulating in online circles since at least 2015.

Logo
The first graphic logo used by Windows was a stylization of a window that was inspired by the tiling window management of Windows 1.0. However, neither the logo nor the corresponding wordmark was used on packaging or within the software itself. The logo was changed in time for Windows 3.0 for a different stylization of a window with black and white gradients used for the window frame and panes, although it was not featured in the product itself either. The only Windows media known to contain both logos as well as a draft version of the 1992 logo is the Windows NT 3.1 build 196 installation disc.

After the success of Windows 3.0, the company sought to create a definite branding for the environment. A draft of the new logo featured in some beta builds of Windows 3.1 already featured the same flag shape as the final version, although the panes were blank, the separators between the panes were thicker and the trail used several shades of blue, cyan, magenta and gray. The final logo used by Windows 3.1 and later uses red, green, blue and yellow for the window pane, with the flag trail continuing the colors of the left-hand side of the window. It is the first one to be used extensively on packaging and within the operating system itself.

Windows 1.x era

 * Win+4
 * Version: Unknown (1.x?)
 * Scheduled to enter development in 1986
 * Project intended to merge Multitasking MS-DOS 4 and Windows "1.1" (Windows 2.0), which was then scheduled for mid-1986. Likely never entered development due to Multitasking MS-DOS 4.0 either failing or being merged into OS/2.

Cairo era

 * Cairo
 * Version: NT 4.00 in 1995, earlier versions unknown
 * Developed 1992-1996, scheduled release date unknown.
 * Development started but project was later scrapped, many of its features were released as part of other versions.

Nashville era

 * Nashville
 * Version: 4.10
 * Developed 1995, scheduled for release in 1996
 * Development started, project goals later transferred to Memphis and Internet Explorer 4.

Windows 2000 era

 * Neptune
 * Version: NT 5.50
 * Developed 1998-1999, scheduled for release in 2001
 * Canceled in January 2000 and replaced with the Whistler project that would later become Windows XP.


 * Triton
 * Scheduled for release in 2001
 * Never left the drafting board, supposed to be a minor update to Neptune, canceled in January 2000.


 * Odyssey
 * According to antitrust documents it was already in development before getting canceled in January 2000.

Whistler era

 * Longhorn
 * Version: NT 6.0
 * Developed 2001-2004, scheduled for release in 2003-2006
 * Initially supposed to be an interim release between Whistler and Blackcomb, the project objectives eventually included a lot of features originally intended for Blackcomb. Development was reset in 2004.


 * Blackcomb
 * Scheduled for release in 2003-2004
 * Originally a major update to Longhorn. Allegedly later renamed to Vienna.

Windows Core OS derivatives

 * Andromeda / Andromeda OS
 * Developed 2016-~2019
 * Scheduled for release in late 2018
 * A Windows Core OS derivative designed to be the operating system running on the Surface Duo (which was codenamed Andromeda). It was canceled in favour of Android during the device's development.


 * Polaris
 * Version: NT 10.0
 * Developed ~2017
 * Scheduled for release in 2018-2019
 * A Windows Core OS based Windows release that would power older desktops and low performance laptops. It was later canceled for unknown reasons.


 * Windows 10X
 * Version: NT 10.0
 * Developed ~2019-2021
 * A version that would have been made for dual-screen devices, later changed to be made for single-screen devices. It was later canceled in favor of integrating key technologies to existing products.