This bonus section takes a look at some of the major features of Drupal 7 and tries to answer how they got there. It will require significant community participation to be complete and is not expected to be ready to be in the book itself.
See http://data.agaric.com/raw/making-drupal-7-historical-overview for some raw material.
The Database Layer
[Larry Garfield interview; needs to be transcribed.]
Getting Real, Getting Dirty, and Getting It Done
The day after a code sprint Dries called and hosted at Acquia, Moshe Weitzman summarized the state of Drupal