apache hadoop versions 2.0 vs. 0.23

Question

There are so many Hadoop versions and different distributions which make me confused. I have a few questions.

1. Apache Hadoop 1.x is from 0.20.205?
2. Apache H

Answer 1

updated answer http://elephantscale.com/hadoop2_handbook/Hadoop_Versions.html

(disclaimer : I am a co-author of this online book)