With z/Architecture®, two facts are prominent: the address space is 16 exabytes in size, and the general purpose registers (GPRs) are 64 bits in length. You can ignore these facts and continue to use storage below the bar. If, however, you want to enhance old programs or design new ones to use the virtual storage above the bar, you will need to use the new Assembler instructions. This section introduces the concepts that provide context for your use of these instructions.