DFU mode is an option in which you can turn on your iPhone in such a configuration that it can interact with iTunes, but it will not boot its operating system or bootloader (this is what really distinguishes this mode from recovery mode). We can say that entering it means updating the firmware of the device.
What is DFU mode usually used for?
The main reason why people need to switch to DFU mode on their mobiles is the need to change the firmware on the device. This can happen for various reasons: the need to return the iPhone and its operating system to its previous state or use the custom firmware that is required for jailbreak or unlock SIM. For example, if you installed a new version of iPhone OS, and then decided that the previous version is preferable for you, you need to reset the new installation using DFU mode.
How to enter DFU mode on iPhone?
Connect your iPhone to your computer and launch iTunes. Turn off the smartphone (hold the power button at the top of the mobile). Press and hold the power or Sleep button at the same time as Home for exactly 10 seconds, and then release the first. Continue to hold Home until a message appears in iTunes indicating that your iPhone in recovery mode has been detected.
When you enter DFU mode, the iPhone screen will be completely black.
Even though the screen becomes dark, this does not mean that the device cannot be synchronized with iTunes or another service (for jailbreaking, etc.).
Remember that if you see the iTunes logo, recovery prompt, or any message on the iPhone screen, you are not in DFU mode. Instead, you started standard recovery mode. Again, the DFU mode is determined only by the presence of a completely black screen on the device. If anything else is happening, repeat the steps above until you switch to the specified mode successfully.
Exit DFU mode on mobile
The easiest way to exit DFU mode is to hold Home and Sleep / power on when connected to iTunes. After that, just press the power button, and this should reboot the device, as usual.
Why are users interested in how to put their gadget into DFU mode?
The most common reason for using DFU mode is jailbreak of the device. Today it is not uncommon among users to buy a new iPhone and find a way to free the device from restrictions on use outside of one network or abroad. This is often due to the fact that people are looking for the cheapest way to purchase an iPhone and are not interested in signing a contract with any particular operator for a long time. Naturally, most users of the device do not want to overpay for roaming or immediately pay the full price of the iPhone to the seller. In other words, there can be many reasons, but they all come down to one thing - the desire to save money and get the most out of it at the lowest cost.
It should be noted that the above instruction does not only work with respect to the iPhone. Similarly, in this mode, you can enter any "apple" device, since the factory settings in them are identical.