DFU or Device Firmware Update is a mode on the iPhone that allows interfacing with iTunes without actually loading the phone's OS.This mode is used mainly to change the firmware on the phone. The DFU mode can, however, be also disabled in the Apple phone depending on the user's requirements. For the procedure to be accomplished, the iPhone must be disconnected from iTunes and it should not be connected to any computer either. Then, with the help of certain keys on the phone, one can exit this mode.
Issue
How I can remove the DFU mode on my iPhone (first gen)?
Solution