Another common usage of firmware downloads is if you have decided you would rather have a prior version of the firmware on your iPhone, you would need to do this through DFU mode, assuming that version of iOS is still signed by Apple. A practical example is if you have an iPhone IPSW file downloaded locally for updating a malfunctioning iPhone, which may require DFU in iTunes to accomplish. In some unique situations, it can also be used to install custom firmware that is required for a jailbreak or SIM unlock.

This can serve to restore a bricked iPhone where updating iOS has failed and the phone is seemingly broken, but it can also be used sometimes to downgrade to a prior iPhone firmware and operating system. The primary reason people need to access DFU mode on their iPhone is to update or change the firmware and iOS on the device, either out of troubleshooting requirements, or personal preference. DFU stands for Device Firmware Update.ĭFU mode is generally intended for advanced use only. 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 the more simple recovery mode).

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