You can then upgrade or downgrade the firmware. Since iPhone upgrades and downgrades involve modifying the IOS as a measure to install third-party apps and preserve baseband firmware, knowing how iPhone DFU mode works is very important. In order to understand DFU Mode better, it is important to understand how it defers from Recovery mode.
The difference is actually all about the iBoot state of the iPhone. Both modes are pre-boot states in Apple mobile devices and they either bypass or use the iBoot state. DFU mode places the iPhone in pre iBoot state which permits the firmware to be upgraded or downgraded. Recovery mode, on the other hand, is the state in the iPhone when software iBoot has loaded, and firmware can only be modified by an upgrade and not a downgrade. From the above explanation, it is safe to assume that iBoot mode sits between DFU mode and Recovery mode.
Phone iBoot (boot loader) is a nifty little bootrom software embedded in the iPhone that first boots, and then allows the general IOS to boot off the iPhone hardware. It is a little like the ROM BIOS which starts up, checks and assesses all hardware components in the personal computer before handing over authority to the main operating system.
The two modes states mentioned above are popular because they are very important pre-IOS installation states. If ever you are to change your iPhone Operating System (IOS) by upgrading, ‘repairing’, or downgrading it, you will definitely have to choose the appropriate of the two states. For example, ‘repairing’ or upgrading the normal IOS from Apple will necessitate that you have your iDevice in Recovery mode. The assumption here is that you care less about changing the device baseband.
If however, you intend to downgrade your iDevice to an earlier IOS version or even modifying its baseband, you definitely will have to go the DFU mode. A device in DFU mode has a black screen and the state cannot be reversed even by connecting it to the computer. As mentioned above, a device in Recovery mode has already gone beyond the initial boot process (iBoot bootloader) and, therefore, hard to manipulate.
In order to bypass the iBoot restrictions and install effect desired modifications, it is best to put your iPod or iPhone in DFU mode. This can be done using the iPhone independently, Redsnow or iREB. Press and hold the power/sleep button for about five seconds till it shows Slide to power off. Go ahead and slide to power off. Press and hold on to the power button for three seconds.
Around now, the Apple logo should appear on the screen. While still holding on to the POWER button, press and hold on to the HOME button for ten more seconds. At about the tenth second, the Apple logo should go off. Release the POWER button and continue holding on to the HOME button for ten to fifteen more seconds.
After this, your iPod or iPhone should be in DFU mode, and to prove this connect it to your computer and see the response. Normally should not boot up. If it does, you probably did not accomplish the process very well. You can start over and try to do it well this time around. Different people have done this a number of times before getting it right. Select Pwned DFU mode in the next window.
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