The course uses two free textbooks. The first is Operating Systems: Three Easy Pieces by Remzi H. Arpaci-Dusseau and Andrea C. Arpaci-Dusseau. The online HTML version is free, but you can also buy the PDF or a printed copy. The second is Concurrent Programming with Harmony by Robbert van Renesse.
Suggested Additional readings:
Supplementary: Those of you looking for a primer/refresher on computer architecture material should read Chapters 3.1-3.11, 4.1-4.5, 5.1-5.3, 7.1-7.4, 8.1-8.5 in "Computer Organization & Design: The Hardware/Software Interface" by Patterson and Hennessy. The chapter numbers are from the 2nd edition -- the library has it, or you can find the content listing online and map it to whatever edition you actually have. Keep in mind that this material is purely supplementary: the tests will focus on the OS side of the content in the course and not on architecture. But there are some overlaps with the OS side of the content and the material covered in these chapters, so it may be helpful to those who may have forgotten it.