> >or a memory-bus timeout due to accessing a location with no storage
> >behind it.
> There is no such thing.  Memory accesses require exactly the same
> amount of time whether there is RAM there or not.

No, God-fearing asynchronous busses like the UNIBUS have a built-in timer
that catches references to non-existant memory.  I believe there have been
more recent instances of this as well.  Modern high-speed busses do tend
to prefer the paradigm of "the memory transaction ends in TWO clock ticks
unless you specifically delay it", though, since it's faster than having
to wait for a specific acknowledge cycle.