Abstract: The computer terminal controller makes it possible to operate a relatively large number of input-output terminals with a single mainframe computer. The controller has a basic configuration enabling it to control up to sixteen terminals. However, the user easily can increase its capacity by adding one or more expansion modules, each module consisting of a cable connector panel and a printed circuit card. Precise locating pins and support structure and hand-operable fasteners are used to mount the panel so that no tools or special skills are needed. Each circuit card preferably contains sufficient circuitry to handle a specific number of additional input/output terminals, and the panel has the same number of cable connectors. The card and the panel are connected to one another by simply plugging them together. The card is guided accurately into engagement with the panel by card guides.