Behind everything else is SUPA Master controller service. This service handles the communications between the various other software components, settings retrieval and storing to and from the main database, status monitoring and updates as well as sending shutdown and power on messages to computers and self service units.

The main schedule also runs on Master controller; thus, Master controller needs to be installed to where it will not be shut down.

There must always be at least one Master controller in a self operated library. One is also the best option; it is possible to have more, but then the data is not shared among all units, which breaks the idea of a single control channel.