If your processor doesn't have special pointer registers, you can use banked memory. (e.g. the high bits are selected on a page-by-page basis by the OS, which

If your processor doesn't have special pointer registers, you can use banked memory. (e.g. the high bits are selected on a page-by-page basis by the OS, which understands 64-bit-wide pointers.) If the processor does have special pointer registers (e.g. 6502, 6809, 8086, AVR, etc.), you use those.