Domain Controller
According to what I read in the wikipedia domain controller is a server that responds to security authentication requests (logging in, checking permissions, etc.) within the Windows Server domain. A Domain is a concept introduced in Windows NT whereby a user may be granted access to a number of computer resources with the use of a single username and password combination.
Active Directory
keep according to what I read in wikipedia, active directory is a directory service that Microsoft developed for Windows domain networks and is included in most Windows Server operating systems as a set of processes and services. An AD domain controller authenticates and authorizes all users and computers in a Windows domain network type — assigning and enforcing security policies for all computers and installing or updating software. For example, when a user logs into a computer that is part of a Windows domain, Active Directory checks the submitted password and determines whether the user is a normal user or system administrator. Active Directory makes use of Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Microsoft's version of DNS, and Kerberos.
So we got a conclusion such as this, the server that functions as the Active Directory Domain, the Server will keep the database of directory information for the domain in question. In a Windows NT-based domain, the database is referred to as the Security Accounts Manager (SAM) database, whereas in Windows 2000, Windows Server 2003, and Windows Longhorn Server, this database is stored in the Active Directory Directory service.
Each domain controller can periodically exchanging directory information by using the process directory replication (replication directory), so the information is owned by each domain controller is always up to date (if the information is stored in a domain controller has expired, the user may get the issue in order to make the process of logging on to the domain controller or find the resources within that domain).
The domain controller has the right to perform authentication against other computers. The domain controller that acts as a central regulator of domain is called the Primary Domain Controller (PDC), while acting as a copy of the PDC is called Backup Domain Controller (BDC).
