Some controller types can be grouped together in a subsystem, for example, 3990 dual frame controllers or 3803s linked via communication cables.
Click on the Group... button in the Edit Controller dialog to open the Group Controllers dialog (see Figure 1). The Independent Controllers listbox lists all controllers of the appropriate type that are currently not grouped. You can move a selected controller into or out of a subsystem; HCM makes the appropriate physical changes. Use the >> and << buttons to move selected items; alternatively, double-click on a controller to move it to the opposite list box.
Figure 1. Group Controllers