Highest order indeed. There is even a very neat scientific article that compares the call graph of the Linux kernel with the "call graph" of the E. Coli genome. The E Coli genome has incredible amounts of copy-paste and legacy code :)

http://blogs.discovermagazine.com/loom/2010/05/03/linux-vers...

http://www.pnas.org/content/107/20/9186.full