This was obviously "bubble" memories have overcome the problem associated with saving the "hard copy" punched paper or magnetic tapes as they are often termed. to the cnc milling machine and horizontal or vertical milling machine. These "bubble" memories refer to the method of charging (ionising) particles to give the "sense" of memory. The "bubble" memories can maintain and retain the part program in their memory for many years without use and degrade very slowly. 

They can be "refreshed" if called into the active memory area and then restored, if necessary, at any time. The main draw-back with storing programs that are not used very often, is that the available memory is soon exhausted and it is usually more profitable under these conditions to save any infrequently used programs in "hard-copy format". 

Recently, some CNC systems have been up-graded to 32-bit microprocessor hard- ware, allowing a degree of artificial intelligence (Al) to be used to overcome and enhance the programming of parts, but more will said about this feature later when we consider part-programming techniques.

Have you got some idea of hard copy in milling machine?