What is DFU mode?
DFU, short for Device Firmware Update, is a special mode that enables a computer to update its firmware. In DFU mode an iPhone can still communicate with iTunes but without iTunes automatically installing the latest version of iOS; it's therefore useful for those running - or installing - older versions of iOS, and for jailbreaking. DFU mode can also be useful when attempting to rescue a non-responsive device that doesn't respond to other less drastic solutions.
(DFU is slightly different to the better-known Recovery Mode, whereby an iPhone is reset to factory settings but with the latest version of iOS.)
You might be wondering what firmware is. As the name suggests, it exists at a level between the hardware (that's your iPhone) and the software - the iOS operating system. Firmware is software that sits inside the hardware and is used to provide various functions at the hardware level.
One function of firmware is to start up the iOS software when you power up an iPhone, which is why updating or restoring the firmware is one way to fix a completely unresponsive phone. It's also used to check the hardware, and to ensure that the right software is working, which is why you'll also need to use DFU mode if you're looking to jailbreak your iPhone (and run software not sanctioned by Apple).
How to put your iPhone into DFU mode
Here's how to put your iPhone into DFU mode. The timing isn't easy, so you may need to try it a couple of times before you get it right.
- Attach your iPhone to a Mac or PC using the USB cable.
- Open iTunes on your Mac or PC.
- Hold down the Sleep/Wake button for about three seconds. The 'Slide to Power Off' screen (above) should appear.
- Slide the switch to turn off the iPhone.
- Wait until the white spinning icon disappears; power-off is now complete.
- Now we activate DFU mode. Press and hold both the Home button and the Sleep/Wake button, and keep them held for 10 seconds. (You need to be reasonably precise with this.)
- When 10 seconds has passed, let go of the Sleep/Wake button, but keep the Home button pressed.
If you do it properly, an alert will appear on your computer saying: "iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes." (The screen of the iPhone will remain turned off - if the Apple logo appears, you've been holding down the two buttons for too long. Start the process again.) Click OK.
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