system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are 12V, 5V and 3.3V so special in electronics?

Is it an industry standard or is there a physics based reason for using these voltages?
gpt
There's nothing special about those voltages. They were simply what worked best at the time.

12 volts is a good voltage to run a DC motor at for fans and spinning hard drives.

5 volts was the original voltage that almost every integrated circuit used. As the fabrication process shrunk they started using 3.3V because a smaller wire needs less voltage. But, they quickly realized that the process of chasing the improvements of chips wasn't going to work and computer components started including voltage regulators that would take an input voltage and convert it to whatever the chip needed instead of relying on the power supply to provide the correct voltage.