CNC control systems generally stand alone near the CNC machine. They act as a translator between your control computer and your CNC machine.
Generally, they add quite a bit of cost to a CNC machine as well. Controllers can cost anywhere from $1000-$20,000 or more depending on their sophistication.
EXPLAINATION OF CNC Control Systems
CNC control systems take your machining instructions from your G-Code and converts the G-Code into motion. You are off to the races. The controller interprets the signal pulses from your Control Computer and instructs the machine to move.
The CNC control system is made up of various electrical parts. Remember earlier that I said some electronic junkies flock to CNC. This is why. CNC control systems can be built if you are savvy with a soldering iron. I myself am not. I personally always default to ordering up a CNC control system from one of my sources.
Control system builders to me are electronic gods. They mix power sources, match up Amp, Volts, etc into the item I need. Generally, you can pick the number of Axis you want before they build the controller. For example, if you are building a CNC Plasma Cutter you may want a two-axis control system. Possibly a three-axis control system if you have a Torch Height Control. If you have a milling machine or a wood router in mind, then a three axis is your ticket. If you want to machine with a rotary axis, then you need a four-axis control system. So on and so forth.