An analog control system permits only one train per cab/block at any one time. A DCC system, however, can be all one electrical block - but many locos can be individually operated simultaneously!
The key advantage of using DCC over traditional analog systems is the elimination of separate blocks for train control. With DCC, many trains be controlled independently within the same electrical block.
Digital Command Control (DCC) is a scheme for controlling locomotives on a model railroad layout. It allows more than one locomotive to occupy the same electrical section of track.
In a segment of DCC-powered track, it is possible to power a single analog model locomotive by itself or in addition to DCC-aware engines through a method known as zero stretching. We won't go into zero stretching here as it can be complex. Not all systems can do this, but many can.
Let's give you the terms so you'll get familiar with them. The most basic Digital Command Control (DCC) system consists of several parts: a throttle, a command station, a booster, a decoder, and a power supply to run it all. Most systems also use a throttle network which allows multiple throttles to talk to the command station. Confused? Don't worry - it won't last!
Let's break this down a little.
The following section is optional to understanding DCC. You are welcome to skip this section and go onto the DCC power section of this tutorial.
The following sections are summaries of devices.
The power supply is just a transformer which supplies low-voltage AC or DC to the Command Station and Booster. Depending on the scale you are operating, you'll need a power supply with various voltages (covered later). For now, just think of the power supply as a transformer that brings down your house power to a level that can be handled by the booster.
The command station is the real intelligence of the DCC system. Typically, the command station is combined with the booster into a single device; however you can buy additional booster-only units for larger layouts that need more power (more trains). The command station contains a microcontroller and is responsible for all communication between the throttles and the decoders. The command station communicates with decoders by transmitting packets of data to them through the rails. Each digital packet tells a train how to run: fast, slow, forwards, backwards, or to turn lights, sound, and other effects on and off.
The booster is sometimes referred to as a the "Power Station" and is responsible for combining the intelligence from the command station with the power of the power supply. Typically, a booster is combined with your first command station. More boosters can been added to layout as demand for power increases.
While the Command Station is the intelligence of the layout, decoders are the "brains" of the locomotive. They monitor the DCC data and listen for commands with their address. Wired between the track and the motor, lights, and sound, these tiny special purpose computers rectify the current to DC and vary the voltage and polarity to provide the motor control, as well as creating any lighting or sound effects they may be capable of performing.
The decoders are programmable, allowing you to change the address, motor performance, and lighting and sound effects. The programming is stored in non-volatile memory - in other words, you don't lose the information when there's no power to the decoder. They can be re-programmed with new information any time you like, and some functions can even be programmed while the train is running, see Decoder Programming for details.
Note: Each decoder is different. There are certain standard functions that they are required to have, but most of the things that make brands and models of decoder different are optional - particularly when it comes to various light and sound effects and fine tuning motor control functions they offer. Check your decoder's capabilities before you by them!