CNC (Computer Numerical Control) is a particular application

usually to control a multi axis machine tool such as a

milling machine or a lathe but also could be a tube bending

machine punch press or similar. The CNC controller is

usually a purpose built controller using a micro computer

but could be a general purpose computer or a PLC. The

forerunner was NC (Numerical Control) before computers were

readily available, it used solid state logic and relays,

timers etc to provide the application.

A PLC (Programable Logic Controller) is a general purpose

logic controller specifically designed to allow the user to

create their own application. They select appropriate I/O

(Inputs Outputs) and perhaps function modules for purposes

such as communications and multi axis servo control and

program the PLC to perform the required functions.