Primary Domain Controller - Definition and Overview

A Primary Domain Controller (PDC) is a server computer in a pre-Windows 2000 NT server Domain. A domain is a concept used in NT server operating systems whereby a user may be granted access to a number of computer resources with the use of a single username and password combination.

Such domains have at the least a Primary Domain Controller, and will often have one or more Backup Domain Controllers. The PDC has the master copy of the user accounts database which it can read and write to. The BDC computers have a copy of this database, but these copies are only 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.

In later releases of Windows, such as Windows 2000, NT 4 type domains have been superceded by Active Directory. In Active Directory domains, the concept of Primary and Backup Domain Controllers doesn't exist. Instead, the domain controllers in these domains are all considered to be equal in that all controllers have full access to the accounts databases stored on their machines.

PDC has been faithfully recreated on the Samba emulation of Microsoft's SMB client/server system.