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What is DCC?
Most literature on Digital Command Control start off like this.  "Digital Command Control is a way to run a lot of trains on your tracks without a whole lot of complicated wiring, toggle switches, and power packs."  All very true!  You take some special throttles, plug it into a "command station/booster", run two wire to your tracks, load up the tracks with locomotives, plug in the power supply, and away you go. 
Then they complicate things by comparing DCC with the good old-fashioned DC power pack! 
Erase the Good-Old-Fashioned DC Power Pack From Your Mind
Forget everything you know about running your layout using the good-old-fashioned DC power pack.  Most magazines, how-to books, websites, and other media compare DCC to DC.  Forget it!  Drop it!  Erase your mind!  Running your layout using a good-old-fashioned DC power pack no longer exists! 
The Networked Computer Network
Now that you've erased you-know-what from your mind, let's take a look at how a bunch of computers, printers, scanners, servers, modems, and other devices are hooked together to form a computer network.  If you work or study in an environment where computers, printers and other devices are connected together in a network, you're well on your way to understanding Digital Command Control. 
The Basic Computer
We have a basic computer in front of us.  We type on the keyboard to enter instructions.  We move the mouse and right-click, left-click or middle-click to enter more instructions.  We get a visual display of what we are doing on our monitor. 
Not all computers have the same capabilities.  Your computer might have a modem, a scanner, a joystick, a printer.  My computer might have more memory, hard drive, more powerful software.  My computer might even be called a "server" or a "mainframe" computer. 
"Hooking Computers Together"
Let's connect your computer and my computer and our friends computer together in a "local area network" or LAN.  This way, we can share resources.  Instead of a whole bunch of small inkjet printers, everyone can use a faster laser printer hooked into our network. We can even add a colour printer to the network, a scanner, a fax machine, a modem, or many other different types of devices to our network. 
This is the power of a networked computer system. 
Recap
So, let's recap all of this. 
  • We have a bunch of computers (with keyboards, mouses, monitors attached), printers, scanners, CD-ROM burners, modems, servers, etc. 
  • Some computers are more powerful than others. 
  • Some computers have extra devices attached. 
  • All of these computers, printers, devices, etc are connected together by a network. 
  • All of these computers, printers, devices, etc communicate with each other through this network. 
We've probably over-simplified the situation - but you get the picture?  If you don't here's a picture for you. 

So What's DCC Got to do with Computers?
Lets apply some of this computer terminology to model railroading. 
  • I have a computer in my hand (we call it a throttle). 
  • On this hand-held computer (the throttle), there's a keyboard, mouse, and monitor (knobs, buttons and display). 
  • This hand-held computer is plugged into a computer network (we call it the Loconet). 
  • I want to send a message (stop, go, increase speed, reverse direction, turn the lights off, ring the bell, blow the horn) from my computer via another computer to your computer. 
  • I turn the knob or push a button on my computer (the throttle), 
  • This sends my message through the network (the Loconet) to a more powerful computer (a command station/booster - more on this later). 
  • This more powerful computer (command station/booster) amplifies and transfers my message along a different part of the network. 
  • Because my message is addressed to your computer, only your computer will pick up my message sent from my computer. 
  • When your computer picks up my message, your computer will carry out the instructions that I sent to your computer. 
  • What does your computer look like in this model railroad scenario?  Why it's your locomotive that you've let me use!
A picture is worth 1,000 words.  Here's our DCC picture. 

That's all DCC is - a networked computer system used to run trains! 
  • Some of these computers are called throttles, 
  • Some of thes computers are called Command Stations/Boosters, 
  • Others are called locomotives. 
  • We can add other computers if we want 
    • - more throttles
    • - more locomotives
    • - whistles, horns, bells
    • - switch machine controls 
    • - signal systems 
    • - etc, etc. 
    • - simply plug them in.
  • Not all of these "computers" have the same capabilities.
The only difference between a computer network and a DCC network are the tracks and the power in the tracks.  Because we need a bit of power to run the locos, the power in the track is typically a continuous 16 volts at 5 amps.  The electricity is alternating current - but not the type you're familiar with.  We won't go into the details at this point - perhaps later on. 
Let's take a look at some "Laws of DCC"