Why computers use binary

3. -Voltage changes based on the loudness or the softness of the music being played.
    - I learned binary is a base 2 system
    - The reason they use a base 2 system is it has the fewest digits

2. -I don't understand why he says you don't buy a cheaper computer.
   - I don't understand why there isn't a base one binary system.

1.- I would like to know more about how the binary affects a computer and if it could run without binary.