How much of the BeOS is portable and how much is tied to a specific processor or hardware architecture?

With that in mind, more than 95 percent of the BeOS has been ported (rather than being re-written from scratch), three times now. The Intel chip is the third processor the BeOS has been implemented on, the PowerPC chip was the second, and AT&T's Hobbit (also called CRISP) processor, which was the basis for our original (and never released) hardware design, was the first.

Read the Be headers for some of the (tongue-in-cheek) possibilities of other processors we're thinking of (hint: check in kernel/OS.h):

http://www.be.com/developers/developer_library/headers/be/index.html