There's also the tried and true Lions' Commentary on UNIX 6th Edition with Source Code pdf floating around to understand what's going on in the workings of a ti

There's also the tried and true Lions' Commentary on UNIX 6th Edition with Source Code pdf floating around to understand what's going on in the workings of a timesharing OS. Nickolai Zeldovich a current MIT professor wrote HiStar OS from scratch and it's source is still available online to view how a minimally trusted system could work http://www.scs.stanford.edu/histar/ http://www.scs.stanford.edu/histar/