Hi All, Thanks for responding to my query. I found an article on the web in which OS is explained on a line to line basis of source code. This is sort of reverse engineering to what I wanted - build the design from code. Posting this message for the curious to know the working of early UNIX operating system. v6.cuzuco.com/home.html. Thanks. __________________________________ Do you Yahoo!? All your favorites on one personal page – Try My Yahoo! http://my.yahoo.com