1) Central 2) Exchange 3) Patchboard 4) Switchboard 5) Telephone exchange 1) Patchboard 2) Switchboard 
A plugboard, or control panel (the term used depended on the application area), is an array of jacks, or hubs, into which patch cords can be inserted to complete an electrical circuit. Control panels were used to direct the operation of some unit record equipment. Plugboards were used on some cipher machines, and some early computers. ==Unit recor...