Regardless of scale, most model trains run from a 12v DC power source. Analogue 12v DC controllers vary the voltage to the track to control speed. Simple to use on basic layouts, each control knob can control a separate track or circuit. Lights, points and signals usually require a separate uncontrolled output.
Digital control (DCC) provides a constant power supply to the track with each locomotive having microprocessor decoder that allows individual control over several trains. A growing number of digital accessories can also provide realistic effects such as synchronised engine noise, lighting and remote point control.