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what is the main difference between external usb devices and other file sharing method?

External USB devices allow the user to put files on it and bring it anywhere they want and still be able to access it. For example, if you put a file on a flash drive, you could access it from any other computer/device.

Another file sharing method is virtual and can easily get lost. For example, if you used iCloud to sync all your photos, you could easily lose them if you forget your password to your account.

I hope this answer helped you! If you have any further questions or concerns, feel free to ask! :)

The difference is the external USB can be removed easier than lets say email share it is just a simple difference