Windows Home Server Release Candidate 1  (June 12, 2007) _[+/-]
Windows redirects here. For the building material, see Window.
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 (GUI).

Versions
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. 16-bit Windows versions include Windows 1.0 (1985), Windows 2.0 (1987) and its close relative Windows/286.

16-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.

Hybrid 16/32-bit operating environments
With the introduction of 32-bit Windows for Workgroups 3.11, Windows could finally stop relying on DOS for file management. Microsoft left little time for Windows Me to become popular before announcing their next version of Windows which would be called Windows XP.

Hybrid 16/32-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. 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. Since then, a new business system, Windows Server 2003, has expanded the top end of the range, and the newly released Windows Vista will complete it. 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.

32-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, 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.

64-bit operating systems

Main article: History of Microsoft Windows History
Security has been a hot topic with Windows for many years, and even Microsoft itself has been the victim of security breaches. Windows was originally designed for ease-of-use on a single-user PC without a network connection, and did not have security features built in from the outset

Security
On 6 January 2005, Microsoft released a beta version of Microsoft AntiSpyware, based upon the previously released Giant AntiSpyware. On 14 February 2006, Microsoft AntiSpyware became Windows Defender with the release of beta 2. Windows Defender is a freeware program designed to protect against spyware and other unwanted software. Windows XP and Windows Server 2003 users who have genuine copies of Microsoft Windows can freely download the program from Microsoft's web site, and Windows Defender ships as part of Windows Vista.

Windows Defender
In an article based on a report by Symantec

Third-party analysis
Current for SP1 and SP2

Timeline of releases
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. Support for Windows 98, Windows 98 Second Edition and Windows Me ended in July 11, 2006, and Extended Support for Windows NT 4.0 ended in December 31, 2004. Security updates were also discontinued for Windows XP 64-bit Edition after the release of the more recent Windows XP Professional x64 Edition.
Windows 2000 is currently in the Extended Support Period, and this period will not end until July 13, 2010. Only security updates will be provided during Extended Support; indicating that no new service packs will be released for Windows 2000.