Organizational Unit:An organizational unit (OU) is a container used to organize objects within one domain into logical administrative groups. An OU can contain objects such as user accounts, groups, computers, printers, applications, shared folders, and other OUs from the same domain. OUs are represented by a folder icon with a book inside. The Domain Controllers OU is created by default when Active Directory is installed to hold new Microsoft Windows Server 2003 domain controllers. OUs can be added to other OUs to form a hierarchical structure; this process is known as nesting OUs. Each domain has its own OU structure—the OU structure within a domain is independent of the OU structures of other domains.There are three reasons for defining an OU:

• To delegate administration – In the Windows Server 2003 operating system, you can delegate administration for the contents of an OU (all users, computers, or resource objects in the OU) by granting administrators specific permissions for an OU on the OU’s access control list.

• To administer Group Policy

• To hide object

Physical Components of Active DirectoryThere are two physical components of Active Directory:

• Domain Controllers

• Sites