If programming a
Commodore 64 ineptly enough that you cause it to
freeze, a
paperclip can be used to
reset the
CPU without losing the contents of
RAM:
Walk around to the back of your C64 so that you are facing the expansion port (leftmost slot when looking at the back of the unit) head-on. The upper surface of the circuit board inside the expansion port is coated with one or two dozen strips of solder. Use a bent paperclip to create an electrical connection between the leftmost strip and the third from the left (you are actually connecting the CPU's reset pin to the DC power supply). Your computer will now display its startup screen and your code will still be in memory. (Of course, if you're writing in BASIC then some extra fiddling will be necessary to convince the interpreter that a program is actually resident.)
Even in the world of modern computers, a paperclip is an invaluable tool; I keep one shoved into a convenient slot in my monitor housing for those situations where my Thinkpad needs a hard reset.