What is the difference between PAL, NTSC, and SECAM?

Question

I know that North America uses NTSC and a majority of the rest of the world use PAL and NTSC, but why?

I put this in the Playstation network because Yahoo Answers put it Tivo's and DVR's but I didn't think that was the right place.

Answer 1

I dont really know why they do it. The whole world should just be one type of format because its one system in all.. They do it because some coutries broadcast tv shows etc in those formats so because of that they have to do this c**p.  

Answer 2

The original reason for the difference is related to the types of AC current adopted in different places.  NTSC is 30 frames per second because it syncs to the 60 Hz used in North American AC power.  There are 60 fields for NTSC video, one for each cycle of the AC power in North America.  In Europe, the power cycles at 50 Hz, so PAL uses 25 fps.  There are other differences like line count and sample rates in the digital space, but the original reason is AC power cycles that are used to sync the signal.  Look it up on Wikipedia, there is a lot of good info there.