1 & 2 pass, 2-pass, 1 single pass

[-=RaDa=-]

What is the difference between these options?

I'm pretty new with divx'ing, and i have always used 1 single pass. ( Divx 5.02 codec ) But is there any difference between this and the other options? Better quality? Faster encoding?

[UncasMS]

2 pass takes almost twice as long but is much better quality