A collection of domains and computers that are managed together. A Microsoft Systems Management Server (SMS) system has one central site and a hierarchy of subsites under it. The central site can be used to manage all other sites.
There are six kinds of SMS sites in an SMS system:
The central site for an SMS system is always a primary site. If you log on to an SMS database for any site to which you have network access and the appropriate permissions, you can administer that site and all its subsites. If you log on to the central site, you can administer your entire network using SMS.