Sugar to carbonate

What's the difference between sugar and co2? I used co2 for my last batch, gives a nice head (maybe a tad excessive, infact) and stays fizzy long enough before needing another.
I've got a batch of Strawberry Cider downstairs and after leaving it to settle, some of it carbonated due to leftover sugar. Tried a bit, and it's not bad, seems more intense than co2 fizz.
So anyway, what's the noticable difference and how much is needed? I've had about 6 pints of the strawberry flat too, so in the barrel it'll be for about 32 pints. How long will this take too?
Cheers.

In the end, adding sugar to carbonate and using CO2 basically are the same. The sugar is eaten by the yeast which then give off CO2. Some folks feel that natural carbonation with sugar gives them a different (better?) effect than carbonating with CO2. Other folks can't tell the difference. It's up to you.

That's cool! Cheers for the info, how much sugar should I add to 32 pints in a 5 gallon barrell and how long will it take to carbonate?