A data access apparatus and a processing system using the same are disclosed herein, which can be a power-off status to permit its storage media being accessible by another processing system. When a bus signal switching and conversion unit receives a first-level control signal, the storage media is permitted to electrically connect only with a first bus channel and to perform a conversion between a first and second bus interface formats to the accessed data and to supply a system power based on a first power signal from the processing system to the storage media. When the bus signal switching and conversion unit receives the second-level control signal, the storage media is permitted to electrically connect only with a second bus channel and to perform a conversion between a second and third bus interface formats to the accessed data, and to supply a system power based on a second power signal from the another processing system to the storage media.