What is iPhone DFU mode?
DFU mode is a state that you can put your iPhone into where it can
interface with iTunes but does not load the iPhone operating system or
boot loader (this is what really differs DFU mode from recovery mode).
DFU stands for Device Firmware Update.
What is DFU mode used for?
The primary reason people need to access DFU mode on their iPhone is
to change the firmware on the device. This can serve to downgrade to a
prior iPhone firmware and operating system, or to use a custom firmware
that is required for a jailbreak or SIM unlock. For instance, if you got
the
iPhone OS 4 download
installed and decided you would rather have a prior version of the
firmware on your iPhone, you would need to do this through DFU mode.
How to enter iPhone DFU mode:-
- Connect the iPhone to your computer and launch iTunes
- Turn the iPhone off (hold down the power button at the top of the iPhone)
- Hold down the sleep/power button and home button together for exactly 10 seconds, then release the power button
- Continue to hold down the Home button until a message appears in iTunes telling you an iPhone in recover mode has been detected
- When you are in DFU mode your iPhone screen will be completely black
Even though the screen is black, that doesn’t mean the device can’t be
interfaced with either iTunes or a custom firmware client (for
jailbreaking, etc).
Remember that if you see the restore logo, iTunes logo, or any
message on the iPhone screen, you are not in DFU mode but standard
Recovery Mode. Again, DFU mode is signified by having a completely black
screen on the device. If anything else is the case, repeat the steps
above until you enter into DFU mode successfully.
Exit DFU mode on iPhone:-
The simplest way to exit out of DFU mode is to hold down the Home and
sleep/power buttons on the iPhone while connected to iTunes. Then just
hit the power button as and this should reboot the device as usual.
And if you’re curious, yes this works all the same on an iPod touch.
The most common use for DFU mode is to jailbreak. It’s not unusual
for people to buy an existing iPhone and jailbreak the device to use the
phone on another network or overseas, this is often a cheaper way to
get an iPhone than to sign into a contract with AT&T, pay roaming
charges, or pay the full iPhone 4 price.