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 are in DFU mode by looking at the device.
What's the difference between DFU and normal recovery mode?
When your iPhone is in normal recovery mode you will see a graphic like this...
(remember, if you see this picture you are NOT in 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 are in DFU mode by looking at the device.
What's the difference between DFU and normal recovery mode?
When your iPhone is in normal recovery mode you will see a graphic like this...
(remember, if you see this picture you are NOT in DFU mode)