What is the abbreviation for active directory? 

Active Directory

Active Directory is a directory service implemented by Microsoft for Windows domain networks. It is included in most Windows Server operating systems. An AD domain controller authenticates and authorizes all users and computers in a Windows domain type network—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 system administrator or normal user. Active Directory makes use of Lightweight Directory Access Protocol versions 2 and 3, Microsoft's version of Kerberos, and DNS.

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