Firmware is probably what you want. Firmware, (as distinct to software and hardware) is a fixed computer programme that is not altered by the user. For example, when the maker of my digital camera believes he has produced an improvement to the operating system inside the camera, he will issue a 'firmware upgrade' and if I copy this into my camera, it will do new things. Similarly for CNC machines, aircraft operating systems and so on. Hope my interpretation of your Q was correct.