PDC stands for Primary Domain Controller. There can be only one PDC in a domain. The PDC holds the main SAM database and provides the main logon authentication for the network. The PDC must be the first server installed on a network. Almost all of the admin work for a network is done at the PDC console.

The PDC feeds the SAM database to the Backup Domain Controllers (BDCs) every five minutes. If the PDC were to crash, a BDC would be able to take over the network until the PDC was fixed and rebooted.

Servers cannot join a new domain without first reinstalling Windows NT.