Computer Numerical control opens up new possibilities and advantages not offered by older NC Machines. some of these are 

1:reduction in the hardware necessary to add a machine function . New functions can be prorammed into the MCU as software.
2.The CNC program can be writen and executed directly at the CNC Machine.
3.Any portion of an entered CNC progream can be played back and edited at will.
Tool motions can be electronically displayed upon playback
4.Many different CNC Programs can be stored in the MCU
5.Several CNC Machines can be linked together to a main computer.Programs written via the main computer can be
downloaded to any CNC machine in the network.this is know as direct numerical control or DNC 
6.Several DNC Sytem can also be networked to form a large distributive numerical control sytem .