This is why http://windows.microsoft.com/en-US/windows/history#T1=era0
Windows XP :-)
Microsoft's OS is Windows.
Windows 7
Windows 7
Microsoft Windows
Microsoft Windows XP is Microsoft's 5th revision of Windows NT. Windows XP is based off Windows 2000 and unified the Home and Business lines of OS. Previously, Windows NT up to Windows 2000 was a business orientated OS while Windows 95 to Windows ME was a home oriented OS. Windows Vista is Microsoft's 6th revision of Windows NT and introduced may new features including updated security and a new graphical user interface caller Aero.
Microsoft DOS, Windows 95, Windows 98, Windows 2000, Windows ME, Windows XP, Windows Vista, Windows 7.
Windows NT is part of the Microsoft Windows line of operating systems. Microsoft Windows is used to describe Microsoft's flagship OS in general while Windows NT is an outdated OS that used to run on workstations and servers. Windows 2000, XP, Vista, and 7 are all based upon Windows NT.
The latest Microsoft Operating System is Windows 7.
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Consumer Windows Family
The "latest" OS released by Microsoft is Windows Server 2008. The latest USER operating system is Vista.