Little brother often helps friends install systems and solve data loss problems. Most of the time, he operates under DOS. Sometimes, when the backed-up data is too large, another hard disk is needed. For convenience and safety, he thought of using a USB external hard disk. Limited by the limited knowledge of DOS, he can't find a solution to use a USB external hard disk under DOS. I hope all the experts can give me some pointers. Thank you in advance here.


