Microsoft Windows

In 1983 Microsoft announced the development of Windows, a graphical user interface (GUI) for its own operating system (MS-DOS), which had shipped for IBM PC and compatible computers since 1981. Since then, Microsoft has shipped many versions of Windows, and the product line has changed from a GUI product to a modern operating system.

Windows 95

• Windows 95 - original release
  
• Windows 95 A - included Windows 95 OSR1 slipstreamed into the installation.
  
• Windows 95 B - (OSR2) included several major enhancements, Internet Explorer (IE) 3.0 and full FAT32 file system support.
  
• Windows 95 B USB - (OSR2.1) included basic USB support.
  
• Windows 95 C - (OSR2.5) included all the above features, plus IE 4.0. This was the last 95 version produced.
  OSR2, OSR2.1, and OSR2.5 were not released to the general public, rather, they were available only to OEMs that would preload the OS onto computers. Some companies sold new hard drives with OSR2 preinstalled (officially justifying this as needed due to the hard drive's capacity).
  The first Microsoft Plus! add-on pack was sold for Windows 95.

Windows 98

On 25 June 1998, Microsoft released Windows 98, which was widely regarded as a minor revision of Windows 95, but generally found to be more stable and reliable than its 1995 predecessor. It included new hardware drivers and better support for the FAT32 file system which allows support for disk partitions larger than the 2 GB maximum accepted by Windows 95. The USB support in Windows 98 is far superior to the token, unreliable support provided by the OEM editions of Windows 95. It also controversially integrated the Internet Explorer browser into the Windows GUI and Windows Explorer file manager, prompting the opening of the United States v. Microsoft case, dealing with the question of whether Microsoft was abusing its hold on the PC operating system market to unfairly compete with companies such as Netscape.
In 1999, Microsoft released Windows 98 Second Edition, an interim release whose most notable feature was the addition of Internet Connection Sharing, which was a form of network address translation, allowing several machines on a LAN (Local Area Network) to share a single Internet connection. Hardware support through device drivers was increased. Many minor problems present in the original Windows 98 were found and fixed which make it, according to many, the most stable release of Windows 9x family.

Windows 2000

Microsoft released Windows 2000, known during its development cycle as Windows NT 5.0, in February 2000. It was successfully deployed both on the server and the workstation markets. Amongst Windows 2000's most significant new features was Active Directory, a near-complete replacement of the NT 4.0 Windows Server domain model, which built on industry-standard technologies like DNS, LDAP, and Kerberos to connect machines to one another. Terminal Services, previously only available as a separate edition of NT 4, was expanded to all server versions. A number of features from Windows 98 were incorporated as well, such as an improved Device Manager, Windows Media Player, and a revised DirectX that made it possible for the first time for many modern games to work on the NT kernel. Windows 2000 is also the last NT-kernel Windows operating system to lack Product Activation.
While Windows 2000 upgrades were available for Windows 95 and Windows 98, it was not intended for home usersIt lacked device drivers for many common consumer devices such as scanners and printers.

Windows 2000 was available in six editions:

• Windows 2000 Professional
  
• Windows 2000 Server
  
• Windows 2000 Advanced Server
  
• Windows 2000 Datacenter Server
  
• Windows 2000 Advanced Server Limited Edition
  
• Windows 2000 Datacenter Server Limited Edition

Windows Millennium Edition (Me)

In September 2000, Microsoft introduced Windows Me (Millennium Edition), which upgraded Windows 98 with enhanced multimedia and Internet features. It also introduced the first version of System Restore, which allowed users to revert their system state to a previous "known-good" point in the case of system failure. System Restore was a notable feature that made its way into Windows XP. The first version of Windows Movie Maker was introduced as well.
Windows Me was conceived as a quick one-year project that served as a stopgap release between Windows 98 and Windows XP. Many of the new features were available from the Windows Update site as updates for older Windows versions, (System Restore and Windows Movie Maker were exceptions). As a result, Windows Me was not acknowledged as a unique Operating System along the lines of 95 or 98. Windows Me was widely criticised for serious stability issues, and for lacking real mode DOS support, to the point of being referred to as the "Mistake Edition" or Me meaning "Many Errors". Windows Me was the last operating system to be based on the Windows 9x (monolithic) kernel and MS-DOS. It is also the last 32-bit release of Microsoft Windows which does not include Product Activation.

Windows XP

In 2001, Microsoft introduced Windows XP (code named "Whistler"). The merging of the Windows NT/2000 and Windows 95/98/Me lines was finally achieved with Windows XP. Windows XP uses the Windows NT 5.1 kernel, marking the entrance of the Windows NT core to the consumer market, to replace the aging 16/32-bit branch. The initial release met with considerable criticism, particularly in the area of security, leading to the release of three major Service Packs. Windows XP SP1 was released in September of 2002, SP2 came out in August, 2004 and SP3 came out in April, 2008. Service Pack 2 provided significant improvements and encouraged widespread adoption of XP among both home and business users. Windows XP lasted longer than any other version of Windows, from 2001 to 2007 when Windows Vista was released to consumers. The Windows XP line of operating systems was succeeded by Windows Vista on 30 January 2007.
Windows XP is available in a number of versions:

• Windows XP Home Edition, for home desktops and laptops (notebooks)
  
• Windows XP Home Edition N, as above, but without a default installation of Windows Media Player, as mandated by a European Union ruling
  
• Windows XP Professional, for business and power users
  
• Windows XP Professional N, as above, but without a default installation of Windows Media Player, as mandated by a European Union ruling
  
• Windows XP Media Center Edition (MCE), released in November 2002 for desktops and notebooks with an emphasis on home entertainment
  
• Windows XP Media Center Edition 2003
  
• Windows XP Media Center Edition 2004
  
• Windows XP Media Center Edition 2005, released on 12 October 2004.
  
• Windows XP Tablet PC Edition, for tablet PCs (PCs with touch screens)
  
• Windows XP Tablet PC Edition 2005
  
• Windows XP Embedded, for embedded systems
  
• Windows XP Starter Edition, for new computer users in developing countries
  
• Windows XP Professional x64 Edition, released on 25 April 2005 for home and workstation systems utilizing 64-bit processors based on the x86-64 instruction set developed by AMD as AMD64; Intel calls their version Intel 64
  
• Windows XP 64-bit Edition, is a version for Intel's Itanium line of processors; maintains 32-bit compatibility solely through a software emulator. It is roughly analogous to
• Windows XP Professional in features. It was discontinued in September 2005 when the last vendor of Itanium workstations stopped shipping Itanium systems marketed as "Workstations".
  
• Windows XP 64-bit Edition 2003, based on the Windows NT 5.2 codebase.

Windows Vista

The current client version of Windows, Windows Vista (codenamed Longhorn) was released on 30 November 2006 to business customers, with consumer versions following on 30 January 2007. Windows Vista intended to have enhanced security by introducing a new restricted user mode called User Account Control, replacing the "administrator-by-default" philosophy of Windows XP. Vista also features new graphics features, the Windows Aero GUI, new applications (such as Windows Calendar, Windows DVD Maker and some new games including Chess, Mahjong, and Purble Place), a revised and more secure version of Internet Explorer, a new version of Windows Media Player, and a large number of underlying architectural changes.
Windows Vista ships in several editions:

• Starter (only available in developing countries)
  
• Home Basic
  
• Home Premium
  
• Business
  
• Enterprise (only available to large businesses and enterprises)
  
• Ultimate (combines both Home Premium and Enterprise)
  

All editions (except Starter edition) are currently available in both 32-bit and 64-bit versions. The biggest advantage of the 64-bit version is breaking the 4 gigabyte memory barrier, which 32-bit computers cannot fully access. In the first year after Vista's release, most installations were still 32-bit, due to poor driver support of the 64-bit version.

Windows 7

Windows 7 is the next major release after Windows Vista and is planned for a three-year development timeframe. It was previously known by the code-names Blackcomb and Vienna.
Some features of Windows 7 are faster boot-up, Device Stage, Windows PowerShell, less obtrusive User Account Control, multi-touch, improved window management, homegroup networking, multiple thumbnails for combined taskbar buttons, and better power management for notebooks. Features included with Windows Vista and not in the Windows 7 Release Candidate include the sidebar (although gadgets remain) and several programs that were removed in favor of downloading their Windows Live counterparts.
On February 3rd, 2009, Microsoft announced that Windows 7 would ship in six editions:

• Starter (available worldwide with new PCs only)
  
• Home Basic (only available to emerging markets)
  
• Home Premium
  
• Professional
  
• Enterprise (only available to volume-license business customers only)
  
• Ultimate (available to retail market with limited availability to OEMs)
  

Microsoft will focus on selling Windows 7 Home Premium and Professional. All editions, except the Starter edition, will be available in both 32-bit and 64-bit versions. According to Paul Thurrott, news editor for Windows IT Pro Magazine, Microsoft plans to ship Windows 7 in 2009.