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.