A Rivendell realm is a set of one or more hosts that utilize a common Rivendell database. Each such realm has its own, independent set of objects, such as cart library, RDCatch event list, set of hosts, etc. Different Rivendell realms are effectively isolated from each other at the application level.

Every physical or virtual computer that is running Rivendell software is referred to as a host. Any host in a Rivendell network can be individually configured and controlled from any other host within the same realm (provided the system administrator has enabled this capability). Hosts can be used for a wide variety of applications, including content ingestion and management, automatic recording (sometimes referred to as "netcatching"), on-air play out or log (sometimes also referred to as a playlist) generation. It is also possible for a single host to perform all of these functions.

Each Rivendell host is a member of precisely one Rivendell realm. Each host within a given realm must be reachable from all other hosts in that realm and reside within the same IP multicast domain. In most cases, this can be ensured by connecting all hosts to the same network switch and configuring them to use the same IP subnet. If this is not feasible, then special arrangements, such as installation of a network bridge or multicast router between the host subnets may be necessary.

Every host on a Rivendell network has one or more users available to it. In this context, a 'user' is merely a set of access policies established by the system administrator that defines what tasks that user is or is not allowed to perform. The set of available users is global to every host in a given Rivendell system; with each host operating under exactly one user at a time. Each host also has one user designated to be the default user. As the name suggests, this is the set of user policies that are loaded by default when the system starts up. It is also possible to change the user currently in use on a given host by running the RDLogin module.

A Rivendell group is a system of categories that is used by the audio library to classify and organize the audio within the library. Groups are a very powerful capability, and many operations within Rivendell can be specified on the basis of group membership. The actual classification scheme, including the number of available groups and their names, is completely arbitrary so as to allow each facility to tailor a schema that best fits its own operational requirements. Designing and implementing the group schema is one of the most important tasks facing the Rivendell system administrator, as a well-designed schema can make long-term maintenance and management of the system substantially easier vis-a-vis a poorly thought out one. We will cover groups in detail in the chapters devoted to the RDLibrary and RDAdmin modules.

Every facility at which Rivendell is deployed is presumed to have one or more ultimate destinations for which audio is intended. These could be radio stations --e.g. WAVA--, satellite uplink channels, live Internet audio streams, or any mix of the above. Each of these sorts of destinations is referred to in Rivendell as a service, and certain parameters, particularly as regards audio play out and log (playlist) creation, can be configured on the basis of what particular service is being referenced.

An audio adapter in Rivendell is simply a device or facility for getting audio into and/or out of a host on a realtime basis. Often this will be a sound card, although other possibilities (such as AoIP or direct routing to other audio applications) also exist. The three main classes of audio adapters supported by Rivendell are:

Commonly known in the DOS/Windows world as 'COM ports', serial ports are often used to communicate with outboard gear, such as satellite receivers and audio switchers. Up to eight serial ports can be accessed simultaneously by each Rivendell host.

Because these capabilities are often (although not always) bundled together in the same device, Rivendell lumps GPIO and switcher devices together within the same class. GPIO stands for 'General Purpose Input Output'. As the name implies, these devices can be used to interface to a huge variety of outboard equipment by means of control lines. GPI (General Purpose Input) lines can be used to sense changes in an outboard system's state (and Rivendell programmed to take various actions on the basis of that), while GPO (General Purpose Output) lines can be used to send commands to an outboard system. The actual physical interfacing of GPIO devices is complex and generally beyond the scope of this document. Readers are encouraged to consult a good handbook on radio engineering for more information. A current list of GPIO/Switcher devices supported by Rivendell can be found in Appendix C, Supported GPIO/Switcher Devices.