At least one Microsoft Windows NT Server computer is required to establish a domain. A domain may be a mixture of Microsoft Windows NT Server computers (configured as domain controllers or file/print/application servers), Microsoft Windows NT Workstation computers, LAN Manager 2.x servers, and workstations. There are three types of servers within a domain: the primary domain controller (PDC), the backup domain controllers (BDC), and file/print/application servers. In a mixed Microsoft Windows NT and LAN Manager environment, a Microsoft Windows NT Server computer must be the PDC. The identity of the PDC is not important because the User Manager for Domains administration tool locates the PDC automatically. The PDC holds the master copy of the user database and security policies. The BDCs hold copies of this security information which can be configured to update at regular intervals. Both the PDC and BDCs are used to validate users logging on to the network. The allocation is done on a load-balancing arrangement.