2-stroke vs. 4-stroke?

What is the difference between a 2-stroke and a 4-stroke? All I know is that 2-strokes require mixed fuel. What other differences are there? I've been looking at motoX bikes (Honda of course) and have noticed that CRF (4-strokes) are relatively more expensive than CR (2-strokes) models.

http://science.howstuffworks.com/two-stroke.htm
 
http://www.howstuffworks.com/engine.htm
 
http://www.howstuffworks.com/diesel.htm
 
http://auto.howstuffworks.com/rotary-engine.htm
 
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