Drop c tuning on guitar?

i've seen drop c tuning a few different ways.... i've seen it like this from string 6 to 1....





C F Bb Eb G C





and i've seen it like this from string 6 to 1





C G C F A D





I'm why learn some bullet for my valentine, the tabs said to tune to drop c, but they didnt say what exactly drop c was. i got dethklok tabs and they had it the first way i put. everywhere else i see has it the 2nd way i put it.

Drop c tuning on guitar?
C G C F A D -- Drop-C is the most common, however, many guitarist mess around with tuning to get a different sound. AC/DC-Its a long way to the top, has the standard EADGBE tuned down about 3/4 step....Why? Because they had to have their guitars in tune with the bagpipes!