Back in the ENIAC era, computers were more analog in nature and used very few digital ICs. Today an average Joe’s computer works with multiple voltage levels, people who had seen the SMPS of a CPU would have noticed that your computer requires ±12V, +5V and +3.3V to operate. These voltage levels are very important for a computer; a specific voltage determines the state of the signal (high or low). This high state is accepted by the computer as binary 1 and the low state as binary 0.