"Operating Systems: Three Easy Pieces Remzi H Arpaci-Dusseau, Andrea C Arpaci-Dusseau" It is by one of the coauthors of the Hennessy and Patterson book and it

"Operating Systems: Three Easy Pieces Remzi H Arpaci-Dusseau, Andrea C Arpaci-Dusseau" It is by one of the coauthors of the Hennessy and Patterson book and it is uptodate, well written and free. http://pages.cs.wisc.edu/~remzi/OSTEP/ http://pages.cs.wisc.edu/~remzi/OSTEP/ The book's page also has links to other interesting books on operating systems and lobsters (sic). The author's teaching page links to excellent undergraduate and graduate level OS material. http://pages.cs.wisc.edu/~remzi/teaching/ http://pages.cs.wisc.edu/~remzi/teaching/