Picture a shop floor with many CNC machines, each one needing its part program loaded before it can run. Direct Numerical Control links all of these individual machine controllers to one central computer, which stores every part program and sends the right one down to whichever machine needs it, instead of each machine keeping its own program on a separate tape or memory card. Generating G code is the job of the CAM post processor, and building the 3D geometry is done in the CAD software, DNC does neither of these things. What DNC actually does is tie a whole group of CNC machines back to one shared computer for program management, so that networking role is its primary purpose.