Numerical Control (NC) refers to the use of coded numerical information in the automatic control of equipment. Numerical Control can be defined as a kind of programmable automation in which the process is controlled by numbers, letters & symbols. The numbers letters & symbols are arranged as a "program of instructions" for a particular job. Such a program is called a part program. The alphanumerical data represent relative positions between a workhead & a workpart as well as other instructions needed to operate the machine. The workhead is a cutting tool or other processing apparatus, & the workpart is the object being processed. The major applications of Numerical Control are Machine tool applications, such as drilling, milling, turning, grinding etc., & Non-machine tool applications, such as assembly, Drafting. The most common applications of NC are in machine tool control. The machine tools and processes presently being controlled by powerful computers is termed as Computer numerical control (CNC) Machines. Computer numerical control is defined as an NC system whose Machine Control Unit is based on a dedicated microcomputer rather than on a hard-wired controller.