1. A digital processing system, comprising: a non-volatile memory device configured to store data persistently; a peripheral bus coupled to the non-volatile memory device and configured to support memory access to the non-volatile memory device; and a digital processing unit coupled to the peripheral bus and configured to perform a direct memory access to at least a portion of storage space in the non-volatile memory device as a system memory instead of input/output (“I/O”) device in accordance with extended memory address referenced from a first address field of an instruction executing by the digital processing unit, wherein the digital processing unit further configured to access I/O storage portion of the non-volatile memory device using a virtual address different from the extended address referenced from a second address field of the instruction.