Introduction of Domain,Domain Controller & Active Directory

Domain:-

• Domain is collection of computers defined by administrator which shares a common directory database. Domain has unique name and provides access to centralized user account and groups account maintained by the domain administrators.
• Domain is a logical secure administrative boundary.
• Each domain is identified by a DNS domain name.
• Every domain must contain at least one domain controller. You install a domain controller by installing Active Directory on any member or stand-alone server.
• When you install the first domain controller in your organization, you are creating the first domain (also called the root domain) and the first forest. You can add additional domain controllers to an existing domain to provide fault tolerance, improve service availability, and balance the load of existing domain controllers.
• In windows 2003 & 2008 domain is represented in triangle.

Domain Controller:-

• A domain controller (DC) is a server that responds to security authentication requests within a Windows Server domain. It is a server on a Microsoft Windows or Windows NT network that is responsible for allowing host access to Windows domain resources. 
•  A domain controller is the centerpiece of the Windows Active Directory service. It authenticates users, stores user account information and enforces security policy for a Windows domain.

Active Directory:-

• Active Directory is Directory Service which contains Information of All User Accounts and Shared Resources on a Network.
• Active Directory is a centralized Hierarchical Directory Database

Purpose of Active Directory:-

• Provides User Logon and Authentication Service using Kerberos protocol.
• To Centralize and Decentralize the resource management.
• To centrally organize and manage
  - User Accounts, Computers, Groups, Networks Resources.
• Enables authorized Users to easily locate Network Resources.