
What is DFU mode?
Device Firmware Update (DFU) mode is a special failsafe mode which Apple has built into all of their devices so that they can restored to a stock iOS firmware regardless of the state they may be in. It is implemented at a lower level than the normal recovery mode, which shows the "connect to iTunes cable" graphic on the screen of the iPhone. DFU mode by contrast has a completely blank screen so there is no way to tell you...