This deserves further explanation. Nachos is not a *real* Operating System that you might use on your computer. That is to say, I doubt there are any real systems out in the business world which are running Nachos. Nachos is primarily an educational tool used to teach students about the inner workings of an Operating System.
One of the classes I took for my Masters was "Introduction to Operating Systems". Although we reviewed some of the code used in the GNU/Linux OS we spent the majority of our time working on Nachos. Given a basic Nachos system we (as a group project) had to add a fully functional virtual memory system and then a fully functional file system. The team I was a member of was able to complete both of these projects on time.
I think I learned more about Operating Systems from this one class then I had in all the time I spent as a systems administrator. Interestingly, one of the teachers from this class was also involved in teaching the Architecture class which did not like at all. This class was one of the hardest class I ever loved.