I would like to ask what “Erase all contents and settings” in iOS actually does. After entering the device password and Apple ID password, the device (mine is an iPhone, but I assume that the case on iPads is the same) gets into a mode with an Apple logo and a progress bar. The first progress bar normally fills up (to 100%) in 15 seconds. Then, the screen turns black and another progress bar appears. This process is slower, taking around a minute to finish around 70-80%, then suddenly the progress bar fills up to 100%.
I’m on iOS 11.4.1. I want to know what exactly the device does during these two steps. That is, what is done when the progress bar fills up quickly during the first step, and slowly during the second step? Alternatively, has that been ever disclosed?