What's the lowest level that Nim can navigate or even dive breaking OS-dependant protected modes?

[termer]

You can use Nim anywhere C can be used, so long as you compile with the 
`--os:any` and `-d:useMalloc` flags. From there, it's just a matter of whether 
certain stdlib modules are usable in your environment. If they aren't, don't 
use them and you'll be fine.