Since the SFR's are variant-dependent, I'd say it would probably be incorrect to refer to it as a bank of registers. I think it's a lot clearer to describe it as I/O space, since it differs between variants with different I/O features.

That's just a way of getting one's head around it. It's definitely not a RAM space, though it's been crammed into a place where the RAM space seems as though it ought to fit.

It was an early solution to a then-evolving problem, namely the single-chip microcontroller, with its crappy hardware and its questionable architecture, but a really useful instruction set. I believe that the instruction set is the root of its popularity and longevity.

RE