Backup Domain Controller
Encyclopedia
In Windows NT
4 server
domains., the Backup Domain Controller (BDC) is a computer that has a copy of the user accounts database. Unlike the accounts database on the Primary Domain Controller
(PDC), the BDC database is a read only copy. When changes are made to the master accounts database on the PDC, the PDC pushes the updates down to the BDCs.
Most domains will have at least one BDC, often there are several BDCs in a domain. These domains exist to provide fault tolerance. If the PDC fails, then it can be replaced by a BDC. In such circumstances, an administrator promotes a BDC to be the new PDC. BDCs can also authenticate user logon requests - and take some of the authentication load from the PDC.
When Windows 2000
was released, the NT domain as found in NT 4 and prior versions was replaced by Active Directory
. In Active Directory domains running in native mode
the concept of the primary and backup domain controllers do not exist. In these domains, all domain controllers are considered to be equal. A side effect of this change is the loss of ability to create a "read-only" domain controller. Windows Server 2008 reintroduces this capability.
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
4 server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
domains., the Backup Domain Controller (BDC) is a computer that has a copy of the user accounts database. Unlike the accounts database on the Primary Domain Controller
Primary Domain Controller
A Primary Domain Controller is a server computer in a Windows domain. A domain is a group of computers , where access to a variety of computer resources is controlled by the PDC. Various account types exist in the domain, the most basic is the "guest" or "anonymous login" account...
(PDC), the BDC database is a read only copy. When changes are made to the master accounts database on the PDC, the PDC pushes the updates down to the BDCs.
Most domains will have at least one BDC, often there are several BDCs in a domain. These domains exist to provide fault tolerance. If the PDC fails, then it can be replaced by a BDC. In such circumstances, an administrator promotes a BDC to be the new PDC. BDCs can also authenticate user logon requests - and take some of the authentication load from the PDC.
When Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
was released, the NT domain as found in NT 4 and prior versions was replaced by Active Directory
Active Directory
Active Directory is a directory service created by Microsoft for Windows domain networks. It is included in most Windows Server operating systems. Server computers on which Active Directory is running are called domain controllers....
. In Active Directory domains running in native mode
Native mode
The term native mode or native code is used in computing in two related senses.*to describe something running on a computer natively or in native mode meaning that it is running without any external support as contrasted to running in emulation....
the concept of the primary and backup domain controllers do not exist. In these domains, all domain controllers are considered to be equal. A side effect of this change is the loss of ability to create a "read-only" domain controller. Windows Server 2008 reintroduces this capability.