- Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It is the direct successor to Windows NT 4.0, and was released to manufacturing on December 15, 1999, officially released to retail on February 17, 2000 for all versions, and on September 26, 2000 for Windows 2000 Datacenter Server. It was Microsoft’s primary business-oriented operating system until the introduction of Windows XP Professional in 2001.