Voltage standards? Like 3.3V, 5V etc
5V is commonly known as TTL logic level voltage, 3.3V is commonly known as CMOS logic level voltage. I'm not aware of any special name for 12V

The TTL logic level voltage was set at 5V because that was the lowest voltage they could afford with the current consumption of the device to allow manufacturability and noise proof performance up a certain standard they were after and thought of as acceptable. This is simply what TTL allowed back in the day. With CMOS the voltage could drop and this lowered power consumption, among other things. Today CPUs are powered by even lower voltages in the 1+V range.