Primary Domain Controller - PDCs

PDCs

Domains have at least a Primary Domain Controller, and will often have one or more Backup Domain Controllers (BDCs). The first Windows NT Server in the domain is configured as a primary domain controller (PDC). The User Manager for Domains utility is used to maintain user and group information for the domain using the domain security database on the primary controller. The PDC has the master copy of the user accounts database which it can access and modify. The BDC computers have a copy of this database, but these copies are read-only. The PDC will replicate its account database to the BDCs on a regular basis. The BDCs exist in order to provide a backup to the PDC, and can also be used to authenticate users logging on to the network. If a PDC should fail, one of the BDCs can then be promoted to take its place. The PDC will usually be the first domain controller that was created unless it was replaced by a promoted BDC.