Microsoft Windows
Microsoft Windows is the name of several families of software operating systems by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs). Microsoft Windows eventually came to dominate the world's personal computer market, overtaking Mac OS which had been introduced previously. At the 2004 IDC Directions conference, IDC Vice President Avneesh Saxena stated that Windows had approximately 90% of the client operating system market. The current client version of Windows is Windows Vista. The current server version of Windows is Windows Server 2003. The successor to Windows Server 2003, Windows Server 2008 is currently being beta tested.

# Versions
The term Windows collectively describes any or all of several generations of Microsoft (MS) operating system (OS) products. These products are generally categorized as follows:

## 16-bit operating environments
The early versions of Windows were often thought of as just graphical user interfaces, mostly because they ran on top of MS-DOS and used it for file system services. However even the earliest 16-bit Windows versions already assumed many typical operating system functions, notably having their own executable file format and providing their own device drivers (timer, graphics, printer, mouse, keyboard and sound) for applications. Unlike MS-DOS, Windows allowed users to execute multiple graphical applications at the same time, through cooperative multitasking. Finally, Windows implemented an elaborate, segment-based, software virtual memory scheme which allowed it to run applications larger than available memory: code segments and resources were swapped in and thrown away when memory became scarce, and data segments moved in memory when a given application had relinquished processor control, typically waiting for user input. 16-bit Windows versions include Windows 1.0 (1985), Windows 2.0 (1987) and its close relative Windows/286.

## Hybrid 16/32-bit operating environments
Windows/386 introduced a 32-bit protected mode kernel and virtual machine monitor. For the duration of a Windows session, it created one or more virtual 8086 environments and provided device virtualization for the video card, keyboard, mouse, timer and interrupt controller inside each of them. The user-visible consequence was that it became possible to preemptively multitask multiple MS-DOS environments in separate Windows (graphical applications required switching the window to full screen mode). Windows applications were still multi-tasked cooperatively inside one of such real-mode environments.
Windows 3.0 (1990) and Windows 3.1 (1992) improved the design, mostly because of virtual memory and loadable virtual device drivers (VxDs) which allowed them to share arbitrary devices between multitasked DOS windows. Because of this, Windows applications could now run in 16-bit protected mode (when Windows was running in Standard or 386 Enhanced Mode), which gave them access to several megabytes of memory and removed the obligation to participate in the software virtual memory scheme. They still ran inside the same address space, where the segmented memory provided a degree of protection, and multi-tasked cooperatively. For Windows 3.0, Microsoft also rewrote critical operations from C into assembly, making this release faster and less memory-hungry than its predecessors.

## Hybrid 16/32-bit operating systems
With the introduction of 32-bit Windows for Workgroups 3.11, Windows could finally stop relying on DOS for file management. Leveraging this, Windows 95 introduced Long File Names, reducing the 8.3 filename DOS environment to the role of a boot loader. MS-DOS was now bundled with Windows; this notably made it (partially) aware of long file names when its utilities were run from within Windows. The most important novelty was the possibility of running 32-bit multi-threaded preemptively multitasked graphical programs. However, the necessity of keeping compatibility with 16-bit programs meant the GUI components were still 16-bit only and not fully reentrant, which resulted in reduced performance and stability.
There were three releases of Windows 95 (the first in 1995, then subsequent bug-fix versions in 1996 and 1997, only released to OEMs, which added extra features such as FAT32 and primitive USB support). Microsoft's next OS was Windows 98; there were two versions of this (the first in 1998 and the second, named "Windows 98 Second Edition", in 1999). In 2000, Microsoft released Windows Me (Me standing for Millennium Edition), which used the same core as Windows 98 but adopted the visual appearance of Windows 2000, as well as a new feature called System Restore, allowing the user to set the computer's settings back to an earlier date.  Microsoft left little time for Windows 2000 to become popular before announcing their next version of Windows which would be called Windows XP.

## 32-bit operating systems
This family of Windows systems was fashioned and marketed for higher reliability business use, and was unencumbered by any Microsoft DOS patrimony. The first release was Windows NT 3.1 (1993, numbered "3.1" to match the Windows version and to one-up OS/2 2.1, IBM's flagship OS co-developed by Microsoft and was Windows NT's main competitor at the time), which was followed by NT 3.5 (1994), NT 3.51 (1995), and NT 4.0 (1996); NT 4.0 was the first in this line to implement the Windows 95 user interface. Microsoft then moved to combine their consumer and business operating systems. Their first attempt, Windows 2000, failed to meet their goals, and was released as a business system. The home consumer edition of Windows 2000, codenamed "Windows Neptune," ceased development and Microsoft released Windows Me in its place. Eventually "Neptune" was merged into their new project, Whistler, which later became Windows XP, which came in both home and professional versions. Then, Windows Server 2003 brought Windows Server up to date with Windows XP. Since then, Windows Vista was released and Windows Server 2008 will bring Windows Server up to date with Windows Vista. Windows CE, Microsoft's offering in the mobile and embedded markets, is also a true 32-bit operating system that offers various services for all sub-operating workstations.

## 64-bit operating systems
Windows NT included support for several different platforms before the x86-based personal computer became dominant in the professional world. Versions of NT from 3.1 to 4.0 supported DEC Alpha and MIPS R4000, which were 64-bit processors, although the operating system treated them as 32-bit processors.
With the introduction of the Intel Itanium architecture, which is referred to as IA-64, Microsoft released new versions of Windows 2000 to support it. Itanium versions of Windows XP and Windows Server 2003 were released at the same time as their mainstream x86 (32-bit) counterparts. On April 25 2005, Microsoft released Windows XP Professional x64 Edition and x64 versions of Windows Server 2003 to support the AMD64/Intel64 (or x64 in Microsoft terminology) architecture. Microsoft dropped support for the Itanium version of Windows XP in 2005. The modern 64-bit Windows family comprises Windows XP Professional x64 Edition for AMD64/Intel64 systems, and Windows Server 2003, in both Itanium and x64 editions. Windows Vista is the first end-user version of Windows that Microsoft has released simultaneously in 32-bit and x64 editions. Windows Vista does not support the Itanium architecture.

# History
Microsoft has taken two parallel routes in operating systems. One route has been the home user and the other has been the professional IT user. The dual route has generally led to the home versions with greater multimedia support and less functionality in networking and security, and professional versions with inferior multimedia support and better networking and security.
The first independent version of Microsoft Windows, version 1.0, released in November 1985, lacked a degree of functionality and achieved little popularity, and was to compete with Apple's own operating system. Windows 1.0 did not provide a complete operating system; rather, it extended MS-DOS. Microsoft Windows version 2.0 was released in November, 1987 and was slightly more popular than its predecessor. Windows 2.03 (release date January 1988) had 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.
Microsoft Windows version 3.0, released in 1990, was the first Microsoft Windows version to achieve broad commercial success, selling 2 million copies in the first six months. It featured improvements to the user interface and to multitasking capabilities. It received a facelift in Windows 3.1, made generally available on March 1, 1992. Windows 3.1 support ended on December 31, 2001.
In July 1993, Microsoft released Windows NT based on a new kernel. NT was considered to be the professional OS and was the first Windows version to utilize preemptive multitasking.. Windows NT and the Windows DOS/9x based line would later be fused together to create Windows XP.
In August 1995, Microsoft released Windows 95, which made further changes to the user interface, and also used preemptive multitasking.   Mainstream support for Windows 95 ended on December 31, 2000 and extended support for Windows 95 ended on December 31, 2001.
The next in line was Microsoft Windows 98 released in June 1998. It was substantially criticized for its slowness and for its unreliability compared with Windows 95, but many of its basic problems were later rectified with the release of Windows 98 Second Edition in 1999. Mainstream support for Windows 98 ended on June 30, 2002 and extended support for Windows 98 ended on July 11, 2006.
As part of its "professional" line, Microsoft released Windows 2000 in February 2000. The consumer version following Windows 98 was Windows Me (Windows Millennium Edition). Released in September 2000, Windows Me attempted to implement a number of new technologies for Microsoft: most notably publicized was "Universal Plug and Play." However, the OS was heavily criticized for its lack of compatibility and stability and it was even rated by PC World as the fourth worst product of all time.
In October 2001, Microsoft released Windows XP, a version built on the Windows NT kernel that also retained the consumer-oriented usability of Windows 95 and its successors. This new version was widely praised in computer magazines. It shipped in two distinct editions, "Home" and "Professional", the former lacking many of the superior security and networking features of the Professional edition. Additionally, the first "Media Center" edition was released in 2002, with an emphasis on support for DVD and TV functionality including program recording and a remote control. Mainstream support for Windows XP will continue until April 14, 2009 and extended support will continue until April 8, 2014.
In April 2003, Windows Server 2003 was introduced, replacing the Windows 2000 line of server products with a number of new features and a strong focus on security; this was followed in December 2005 by Windows Server 2003 R2.
On January 30, 2007 Microsoft released Windows Vista. It contains a number of new features, from a redesigned shell and user interface to significant technical changes, with a particular focus on security features. It is available in a number of different editions, more than any previous version of Windows. It has been subject to several criticisms.

# Timeline of releases

# Windows Lifecycle Policy
Microsoft has stopped releasing updates and hotfixes for many old Windows operating systems, including all versions of Windows 9x and earlier versions of Windows NT. Windows versions prior to XP are no longer supported, with the exception of Windows 2000, which is currently in the Extended Support Period, that will end on July 13, 2010. Windows XP versions prior to SP2 are no longer supported as well. Also, support for Windows XP 64-bit Edition ended after the release of the more recent Windows XP Professional x64 Edition. However, it is possible for users of older, now unsupported versions of Windows to download and install updates, by going to the Windows Update catalog.

# Emulation software
Emulation allows the use of some Windows applications without using Microsoft Windows. These include:
- Wine - an almost-complete free software/open-source software implementation of the Windows API, allowing one to run most Windows applications on x86-based platforms, including GNU/Linux. Wine is technically not an emulator; an emulator effectively 'pretends' to be a different CPU, while Wine makes use of Windows-style APIs to 'simulate' the Windows environment directly.
- CrossOver - A Wine package with licensed fonts. Its developers are regular contributors to Wine, and focus on Wine running officially supported applications.
- Cedega - TransGaming Technologies' proprietary fork of Wine, which is designed specifically for running games written for Microsoft Windows under GNU/Linux.
- ReactOS - An open-source OS that intends to run the same software as Windows, at an early alpha stage.
- Darwine - This project intends to port and develop Wine as well as other supporting tools that will allow Darwin and Mac OS X users to run Microsoft Windows applications, and to provide Win32 API compatibility at application source code level.