List of Microsoft's Operating System Releases

• Xenix (licensed version of Unix; licensed to SCO in 1987)
• MSX-DOS (developed by MS Japan for the MSX 8-bit computer)
• MS-DOS (developed jointly with IBM, versions 1.0–6.22)
  • Windows 1.0 (Windows 1 - Based on Visi On) April 30, 1985
  • Windows 2.0 (Windows 2) December 9, 1987
  • Windows 3.0 (Windows 3 - Is the first version of Windows to make substantial commercial impact) May 22, 1990
  • Windows 3.1x (Windows 3.1) March 18, 1992
  • Windows 3.2 (Chinese-only release) November 19, 1992
  • Windows for Workgroups 3.11 January 21, 1993
  • Windows 95 (Codename Chicago - Windows 4.0) August 24, 1995
  • Windows 98 (Codename Memphis - Windows 4.1) June 25, 1998
  • Windows Millennium Edition (Windows Me - Windows 4.9) September 14, 2000
• Windows NT (Full 32-bit kernel, not dependent on MS-DOS)
  • Windows NT 3.1 July 27, 1993
  • Windows NT 3.5 September 21, 1994
  • Windows NT 3.51 May 30, 1995
  • Windows NT 4.0 July 31, 1996
  • Windows 2000 (Windows NT 5.0), February 17, 2000
  • Windows XP (Windows NT 5.1) October 25, 2001
  • Windows Server 2003 (Windows NT 5.2) April 24, 2003
  • Windows Fundamentals for Legacy PCs (based on Windows XP) July 8, 2006
  • Windows Vista (Windows NT 6.0) January 31, 2007
  • Windows Azure (based on Windows Vista) 2009
  • Windows Home Server (based on Windows Server 2003) February 28, 2008
  • Windows Server 2008 (based on Windows Vista) February 28, 2008
  • Windows 7 (Windows NT 6.1) October 22, 2009
  • Windows Server 2008 R2 (based on Windows 7) October 22, 2009
  • Windows Home Server 2011 (based on Windows Server 2008 R2) April 6, 2011
  • Windows 8 Consumer Preview (First downloadable release) March 1, 2012
  • Windows 8 Server Beta (First downloadable release) March 15, 2012
• Windows CE (OS for handhelds, embedded devices, and real-time applications that is similar to other versions of Windows) November, 1996
  • Windows CE 3.0 December 25, 2002
  • Windows CE 5.0 February 27, 2004
  • Windows CE 6.0 May 5, 2004
  • Windows Mobile (based on Windows CE, but for a smaller form factor) April 14, 2005
  • Windows Phone October 21, 2010
• Singularity - A research operating system written mostly in managed code (C#) November 30, 2009
• Midori - A managed code operating system July 21, 2010
• Xbox and Xbox 360 OS custom operating systems May 12, 2005 and August 10, 2006