A server running Microsoft Windows NT or Windows 2000 that is not a domain controller. A member server does not contain a copy of the domain directory database or Security Account Manager (SAM) database; it has its own local security database.
Member servers can participate in domain security, which allows files and other resources on the member server to be shared and permissions to be assigned to different domain users and groups. However, you cannot use member servers to authenticate user credentials, as you can with domain controllers.
Member servers are usually used for dedicated network purposes such as the following:
On Windows 2000–based networks, a member server is a server that stores Active Directory information and is not a domain controller. However, in Windows 2000 you can change a member server to a domain controller by using the Active Directory Installation Wizard.