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

Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Windows 2000 for high-end and business users and Windows Me for home users, and is available for any devices running Windows NT 4.0, Windows 98, Windows 2000, or Windows Me that meet the new Windows XP system requirements.