mysql: about index

I am making my term paper now.My rearch topic is Mysql.I have read the code of mysql.But I really don't know how mysql compresses his index.And which structure mysql used to store his index.I hope there is someone who can answer my question.
Thank you very much.

red_apple,
Beijing,China

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red_apple

I hope my answer can be helpful.
I wondered when I read Mysql Manual.
It says how mysql work!
memory and disk and so on.
I interested in turning.
I think you can get an idea in the manual.