A version of Microsoft's Windows operating system. Most users of Windows 98 and Windows NT moved to Windows 2000. Previously called Windows NT 5.0, Microsoft emphasized that Windows 2000 was evolutionary and "Built on NT Technology." Windows 2000 was designed to appeal to small business and professional users as well as to the more technical and larger business market for which the NT was designed. The initial Windows 2000 product line consisted of four products: Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server and Windows 2000 Datacenter Server. [Microsoft Windows]