DFU (pronounced Say-ef-iu) of the acronym in English "Device Firmware Update" is the mode in which the iDevice (iPhone / iPod Touch) is placed to recover (make a "recovery") team. But what is the difference Recovery Mode and DFU? DFU mode, the unsuccessful iDevice iBoot service (Bootrom), who is responsible for verifying the legitimacy of the firmware version installed and if the version is equal to or greater installed. In this way, you can place a customized or an earlier version firmware.
The steps to put your iDevice in DFU mode are:
1. Connect the device to the computer using the USB cable.
2. Shut down the computer.
3. Leave the power button (POWER) and HOME tight for ten (10) seconds.
4. Release the power button and stay tight HOME button until the computer recognizes the device.
5. Unlike recovery mode where get an iTunes logo in DFU mode the screen will remain black but can still interact with the computer from iTunes.