CAD (Computer-Aided Design) and CAM (Computer-Aided Manufacturing) systems are primarily hardware-oriented, but the software aspect is what gives them the functionality to carry out design and manufacturing tasks. Without software, the hardware would lack the necessary instructions to operate effectively, essentially "giving life" to the system.
- Numerical control refers to the automated control of machining tools by means of a computer. While important, it is not the key element that gives CAD/CAM systems life.
- Documentation is crucial for organizing and managing design and manufacturing processes, but it does not directly relate to the functionality of CAD/CAM systems.
- Communications is a general concept important for data exchange, but software specifically enables the operation of CAD/CAM systems.
Thus, the correct answer is (3), Software.