Required knowledge for creating an os

Look here, it raises some points that I'd otherwise have to type.
 
http://www.daniweb.com/software-development/computer-science/threads/4894/designing-an-operating-system[^]
 
Best place to go is probably the Linux kernel site, http://www.kernel.org/[^]
 
this will help as well
 
http://www.linuxfromscratch.org/[^]
 

Understand, even when all the source is available, it's a complex task to build and create a working operating system!

One more resource is the book "Operating Systems: Design and Implementation 3/e" by Tanenbaum. This guides you through the innards of an operating system called Minix3[^]
 
(Note: I have no first hand experience with either the book or Minix itself, but I see good reviews of that book).