"Programs like SLOCCount can be used to inspect the
Linux kernel's source code in more detail. According to this tool,
the source code line count is not 9 million but exactly 6,399,191
(Source Lines of Code/SLOC), as the program doesn't count blank
lines, comments and several other types of input. More than half of
the lines are part of hardware drivers; the second largest chunk is
the arch/ directory which contains the source code of the various
architectures supported by Linux."