The directory system agent (DSA) is a collection of services and processes that run on each Windows 2000 Server and later domain controller and provides access to the data store. The data store is the physical store of directory data located on a hard disk. In Active Directory Domain Services, the DSA is part of the local system authority (LSA) subsystem. Clients access the directory using one of the following mechanisms supported by the DSA:

• LDAP clients connect to the DSA using the Lightweight Directory Access Protocol (LDAP). Active Directory Domain Services support LDAP 3.0, defined by RFC 3377, and LDAP 2.0, defined by RFC 1777. The Active Directory Client Extension and Windows 2000 and later clients use LDAP 3.0 to connect to the DSA.
• Windows NT and earlier clients not using the Active Directory Client Extension connect to the DSA using the Security Account Manager (SAM) interface.
• MAPI clients such as Microsoft Exchange Server connect to the DSA using the MAPI remote procedure call interface.
• The DSAs in Active Directory Domain Services connect to each other to perform replication using a proprietary remote procedure call interface.

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Build date: 11/12/2009