http://www.personal.kent.edu/~rmuhamma/OpSystems/os.html
http://www.wannalearn.com/Computers_and_the_Internet/Operating_Systems/
http://viralpatel.net/taj/operating-system-tutorial.php
http://www.softwaretrainingtutorials.com/operating.php
http://www.softlookup.com/tutorial/os.asp
http://www.ee.surrey.ac.uk/Teaching/Unix/