References

http://www.computerhope.com/os.htm#03

http://www.webopedia.com/TERM/O/operating_system.html

http://www.wisegeek.org/what-is-an-operating-system.htm

http://www.blurtit.com/q576576.html

ftp://ftp.awl.com/cseng/authors/silberschatz/OS4E/tm01-05.pdf