CNC stand for Computer Numerical Control, and refers specifically to the computer control of machine tools. The main purpose of CNC Milling Machines is to repeatedly manufacture complex parts in metal as well as other materials, using a specially coded program. This specially coded program that is used by CNC Milling machines is written in a notation called G-code. G-codes represent specific CNC Milling functions in alphanumeric format. CNC Milling was developed in the late 1940's and early 1950's by the MIT Servomechanism Laboratory.