The whole of Plan9 is written like that. If you look here http://plan9.bell-labs.com/sources/plan9/sys/src/9/ http://plan9.bell-labs.com/sources/plan9/sys/src/

The whole of Plan9 is written like that. If you look here http://plan9.bell-labs.com/sources/plan9/sys/src/9/ http://plan9.bell-labs.com/sources/plan9/sys/src/9/ You can see that port & boot are the portable code. Each architecture can fall back on that less optimised code should it need to. Then each of the directories: bcm, kw, mtx, omap, pc, pcboot, ppc, rb, teg have platform specific c files This greatly eases porting to a new architecture and also means cross compilation is significantly easier. #ifdefs are rare in the source code and other pragmas are few and far between. Conditional compilation is the enemy of readable code.