Windows NT was Microsoft's first industrial-strength network operating system. It went through four major revisions before being replaced with Windows 2000. It was originally designed for small to medium-sized networks. It provided users with file and printer sharing, a web server using the familiar Windows 95 interface. Windows NT 4 is still widely used because of the cost of upgrading to Windows 2000 Server and the reluctance of many network administrators to move to Windows 2000 until Windows 2000 has been in use for a longer period of time.