Spinellis has written a good paper for the “30th International Conference on Software
Engineering” (ICSE ’08) that looks at the code quality of the source codes of Windows (WRK –
Research Kernel based on Windows Server 2003), Linux, Solaris and FreeBSD.
Diomidis has analyzed the source codes of these 4 kernels and uses some code
metrics, in order to measure the quality of each kernel in each area.
For those, who don’t like reading lengthy texts, a summary
of the results is at the end (section 5: summary and discussion). Each operating system has its own strengths and weaknesses, so there is no clear winner.
The paper can be found at http://www.spinellis.gr/pubs/conf/2008-ICSE-4kernel/html/Spi08b.pdf
and all the queries for the code analysis can be found at http://www.spinellis.gr/sw/4kernel/.
Finally, Diomidis has a very lengthy list of classic reads at his website.