Windows 2000 ( also known as Win2K , W2K or Windows NT 5.0 ) is an operating system that was designed to work with computers that have either single or multiple processors . Windows 2000 is a continuation of the Microsoft Windows NT family of operating systems , replacing Windows NT 4.0 . Originally called Windows NT 5.0 , then Windows NT 2000 , Microsoft changed the name to Windows 2000 on 27 October 1998 .