No need for different password.
The user can be authenticated with the same password for the DCs of a domain.
No, you do not. You only install Active Directory if the system is going to be a domain controller. If it is a member server or a standalone server Active Directory should not be installed.
Domain controller is the physical object.
The Restartable Active Directory, that allows you to have the ntds.dit in offline mode WITHOUT rebooting the domain controller.
The Active Directory database is stored on each domain controller in a file called NTDS.DIT
Repair or recover Active Directory.
In Windows Server 2011 it is called Active Directory.
Domain Controller
Restartable Active Directory
NTDS.DIT
You run the 'dcpromo' command to remove active directory and demote a domain controller to a member server. To remove AD completely you would have to do this process on all domain controllers.
An AD-integrated zone is a DNS zone that is integrated with Active Directory. Typically this occurs on a Domain Controller (dc), which requires DNS to answer queries from Active Directory (LDAP).
Directory Services Restore Mode (DSRM)tryrestartable Active Directory feature, which allows you to place the ndts.dit file in a offline mode without rebooting the domain controller outright.