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I was seeing ledger nano ads and confused how bitcoins are stored on such a usb. Now i see its just a key file stored into it, and all rest are just extras.
Sure, but those "just extras" are pretty important... They make sure that master private key never ever leaves the hardware wallet... That's a pretty big deal, not something you should just catalog as "just extras".
By this defenition, a car is just four wheels and an engine. The steering wheel, chassis, airbags,... are just extra's.... They add nothing to the basic functionality of your car...
Well, I agree with that. I didn't meant they aren't important, If i mean so, I would mentioned that

.
I meant the device as a combination, not from "important" view.