What happens in this example case?

Hi, it would be good if someone explained how is git doing things internally when:

1. mkdir dir; cd dir; git init; echo -e "A\na\nA" > file; git add .; git commit -a -m comm1

2. echo -e "A\nb\nA" > file; git commit -a -m comm2;

I want to understand how those three letters are stored in each of the two cases and how can the contents of file be recovered from .git archive, say, after git reset --hard <commit-hash>?

(is git storing just the position of change for 'b' and 'b' in the second case? why is $(git cat-file -p) showing all three letters for the respective objects in both cases?)