CipherLab RK25 Reference Manual page 75

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SD card as internal storage in Storage Settings page
The SD card is used for storing anything on this device only, including apps and photos.
Requires formatting that prevents it from working with other devices.
SET UP SD CARD AS PORTABLE STORAGE
Using SD card as a portable device allows you to treat it as a USB disk, by swapping it
between your Android device and the computer to easily transfer files. This is quite handy
when there is a need to offload files that are taking up too much storage space.
When this device is connected with PC, the disk content is readable from PC client:
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Using RK25 Mobile Computer