DCC - digital command control - is a control system for the model railway where a decoder onboard the locomotive is used to provide control of speed and direction of the motor. The instructions are passed from the 'throttle' to the decoder by means of digital signals that are superimposed over a constant track voltage. Put simply, you control the locomotive and not the track.
As well as output to power the motor, many decoders also have a number of auxiliary outputs that can power other functions: lights or smoke for example, and really fancy decoders also have sound.
As there is always voltage at the track these functions are not related to train speed as happens with lights on direct current (DC) controlled trains.
There are also decoders that will power stationary operations - points, signals, etc. - all from the same handset as you run your locomotive.
DCC means that separate power sections and isolating switches are completely eliminated. No more of those cunning control schemes that electrical experts come up with to pass trains around a big layout. As the whole layout is live you set your route and drive there. Stop trains where you want and move control to another. Put two trains to a platform at the station like the real thing. Put three in the same siding in the engine shed.
DCC systems allow double heading, and typical 'real railway' moves like adding a pilot engine or joining multiple units can be done with ease. As there is now absolutely nothing to stop trains being driven into one another, on a medium to large layout with several operators you are likely to need a signalling system to drive by, and maybe another operator to be signalman!At the moment DCC is taking off rapidly amongst modellers in this country. Currently locomotives are being sold that have sockets and space to accept a decoder. We believe that it won't be long before models of British locomotives are sold with the decoder factory fitted: American and European models already are.