A domain controller is a server within Microsoft Windows or Windows NT that responds to security authentication requests including log in and checking rights such as accessing a file folder and file modification. It manages all the security requests from other machines and servers on the Windows Server domain.
Generally, a domain controller hosts one domain directory partition containing data about the domain in which it is located. Domain controller technology was first introduced in Windows NT, and allowed users to access multiple computers using the same login credentials. It enabled the host to access Windows domain resources. In Windows NT, domain controller consists of both primary domain controller and a backup domain controller. The principal role of primary domain controller is to cushion the system against slow down or crashing as a result of overloading from management of other operations and security requests. The backup domain controller assumes the functions of primary domain controller in case the latter breaks down.
A computer installed with Windows Server can be configured with a particular server role. A domain controller acts as the centerpiece of Active Directory service which stores user’s account information. It also acts as security enforcer for Windows domain. The introduction of Active Directory nearly replaced the role of primary and backup domain controllers.