D: E: etc just get assigned as you added drives. D: was usually the CD drive because usually people only had 1 hard drive. I had 3 at one point and my CD drive was F:

Ha! After reading this i realized i was singing Indiana Jones in my head instead of the a team song

Electricity in the usa is not weaker than Europe. Since the voltage is half as high, it just takes double the current to do the same work. A heater running 220v at 5 amps and a heater running 110v 10 amps will work exactly the same.