A Cluster Controller is a central unit of a multi-user system, which is referred to in German as Gruppensteuerung or Mehrfachsteuerung.
The classic cluster controller takes over the communication control of multiple, dumb terminals or workstations in a terminal network. This often refers to a controller of the IBM 3170 family, for example the IBM 3174 or a compatible one. The cluster controller, in turn, is connected via a data line to a front-end processor (FEP) that regulates data traffic between the cluster controller and the mainframe. The Cluster Controller can be connected to the frontend processor or host either via a channel or via an SDLC connection.