UNIX

“A Commentary on the Sixth Edition UNIX Operating System” by John Lion
http://www.lemis.com/grog/Documentation/Lions/index.html

UNIX Operating System Source Code Level Six
http://v6.cuzuco.com/

BSD

020163354X TCP/IP Illustrated, Volume 2: The Implementation

Linux

Understanding the Linux Virtual Memory Manager
http://www.phptr.com/content/images/0131453483/downloads/gorman_book.pdf

Donald Knuth

0201134373 Computers & Typesetting, Volume B: TeX: The Program

0201134381 Computers & Typesetting, Volume D : Metafont: The Program

MySQL

MySQL Internals Manual
http://dev.mysql.com/doc/internals/en/