为存储磁盘或U盘更换盘符。比如：U盘插在PC机上显示的是F盘，可以被更换成H、G直到Z盘，只要该盘符空闲。-U for the storage disk or disk drive replacement. For example: U disk inserted in the PC, shows the F disk, can be replaced H, G until the Z disk, as long as the drive is idle.