The realization that the operating systems of the target machines were as great an obstacle to portability as their hardware architecture led us to a seemingly radical suggestion: to evade that part of the problem altogether by moving the operating system itself.
—Portability of C Programs and the UNIX System (1978)
Unix was the first production operating system to be ported between differing processor families (Version 6 Unix, 1976–77). Today, Unix is routinely ported to every new machine powerful enough to sport a memory-management unit. Unix applications are routinely moved between Unixes running on wildly differing hardware; in fact, it is unheard of for a port to fail.