See also "xv6" (http://pdos.csail.mit.edu/6.828/2010/xv6-book/index.html http://pdos.csail.mit.edu/6.828/2010/xv6-book/index.html), (roughly) a reimplementation

See also "xv6" (http://pdos.csail.mit.edu/6.828/2010/xv6-book/index.html http://pdos.csail.mit.edu/6.828/2010/xv6-book/index.html), (roughly) a reimplementation of v6 UNIX for SMP x86 used by MIT's operating systems class. They're even writing their own version of Lions' Commentary for it.