You can do this on most microprocessors just by leaving the address lines uninterpreted. On the 68000 the top 8 lines were flapping in the breeze, so you could

You can do this on most microprocessors just by leaving the address lines uninterpreted. On the 68000 the top 8 lines were flapping in the breeze, so you could use those bits for anything and still dereference the same object. The first MacOS used those bits for some things; notably desk accessories. It took them years to kill that practice so that later virtual memory versions of the Mac would work. IBM made a similar mistake in OS/360 (24 bit address space, 32-bit pointer values . . . that was very bad).