A domain controllers is a server which acknowledges authentication requests and validates users access on the computer network in order to use the resources.
This is done by the domain controller by verifying the username and password.
It also allows user to access the other domain and also access the resources of other domain.
For example there is a network of multiple computers and each computer requires authentication i.e user is asked to provide the username and password.
Authenticating every computer and managing is not easy so a computer is appointed this task of authentication other computers.
This computer is called domain controller which can easily maintain these authentication details of the users.
The authentication information (login details) of users, computers and shared resources is saved in Active Directory database.
If a user requests access to the resource via login then the login details (username and password) of the user should match with that stored in the Active Directory in order to grant access to the user.
Domain controller enables resources sharing and is good for large networks and provides with improved security.
