The classic cluster controller takes over the communication control of several, 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, for its part, 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.
In addition, there are cluster controllers with extended functionality, advanced cluster controllers, the so-called subhosts. Advanced Cluster Controllers have an operating system and are freely programmable, they enable communication and support application programs.