Hi,
Why can't we understand?
Let's make it more visible with a similar question:
I have a vehicle. How long will it take to go to house_xx in London with it?
London is the target .... in your case the file.
The vehicle ... in your case is USB.
But there are many different vehicles. A bicycle, a car, a train, an aeroplane...
With a bicycle you my go to the house directely...with a train or an aeroplane you need an additional transport system to go to the house.
It's similar with USB devices. Some are made for file transfer, some are not ... and need additional effort.
Some are made for special files, like audio, and they are not suitable for a text file.
Some need special software for file transfer .... managing the protocol, like XModem (transfering file name, data, error detection...)
Klaus