During the boot-up process, if one step is unable to load or verify the next step, then the boot-up is stopped and the iPhone displays the screen shown in the following screenshot:

This mode is known as recovery mode and is required to perform upgrades or restore the iPhone. To enter recovery mode, perform the following steps:

1. Turn off the device.
2. Hold down the iPhone Home button and connect the device to a computer via a USB cable. The device should turn on.
3. Continue holding the Home button until the Connect to iTunes screen appears. Then, you can release the Home button (on a jailbroken iOS device, this screen may appear with different icons). Most forensic tools and extraction methods will alert you regarding the current state of the iOS device.
4. To exit recovery mode, reboot the iPhone. On iPhone 6s and earlier, this can be completed by holding down the Home and Sleep/Power buttons until the Apple logo appears. On iPhone 7 and iPhone 7 Plus, this can be done by holding the Side button and Volume Down button together. On iPhone 8 and later, you do this by clicking the Volume Up button, then clicking the Volume Down button, and then holding down the Side button.

Normally, the process of rebooting returns the iPhone from recovery mode to normal mode. This same methodology applies to the Apple Watch. You may experience a situation where the iPhone constantly reboots into recovery mode. This is known as a recovery loop. A recovery loop may occur when the user or examiner attempts to jailbreak the iOS device and an error occurs. To get the device out of a recovery loop, the device must be connected to iTunes so that a backup can be restored to the device.