Updated Operating Systems Resource (#2200)

* Updated Operating Systems Resource

* Updated Operating Systems resource

free-programming-books.md

@@ -550,6 +550,7 @@
 * [Computer Science from the Bottom Up](http://www.bottomupcs.com)
 * [How to Make a Computer Operating System (Work in Progress)](https://github.com/SamyPesse/How-to-Make-a-Computer-Operating-System)
 * [Operating Systems and Middleware](https://gustavus.edu/mcs/max/os-book/) (PDF and LaTeX)
+* [Operating Systems Concept 9th edition](http://codex.cs.yale.edu/avi/os-book/OS9/slide-dir/) - Avi Silberschatz, Peter Baer, Galvin Greg Gagne (PDF)
 * [Operating Systems: Three Easy Pieces](http://pages.cs.wisc.edu/~remzi/OSTEP/) (PDF)
 * [Practical File System Design: The Be File System](http://www.nobius.org/~dbg/practical-file-system-design.pdf) - Dominic Giampaolo (PDF)
 * [The Art of Unix Programming](http://catb.org/esr/writings/taoup/html/) - Eric S. Raymond