Installing iOS update

I don't have Developer documentation, as it would take a while to sift through, but to my knowledge, it doesn't wipe the old operating system. It acts similar to update the OS on a Mac. It is a full operating system, and it layers the new OS on top of the old one. If you do the update directly through your phone, it would not be able to update the devices if it was wiping it clean, as it would wipe the update as well. I believe the iTunes updates act the same way.

Cheers!

iTunes does in fact download the complete update package but does not wipe the device clean. It will replace files and parts of the OS with updated versions while retaining the non updated or modified files, and all user data.

The only time iTunes wipes the device, is when you restore the device to factory condition. It will then remove everything from the device, and install a clean OS version.

If done directly on the device(without itunes), it will remove the relevant updated files and sections of the OS, and replaces them with the updated versions.

It does not as suggested "lay" the update on top of the old OS. It modifies the existing OS with the new and updated files from the update. As such it may use a bit more storage space, if the new parts are a bit bigger than the old one, but generally it takes over the space used by old files.

With that said, I do not believe Apple has any documentation regarding the exact operation of iOS updates. But it is the general operation of updates on any platform.

Don't quite understand the question. Can you rephrase it?

iTunes will show "installing firmware" as part of the iOS software update. The firmware is the base iOS runs on. When updating the iOS software, it may need to update the firmware as well to get it ready to boot the new version of iOS if required. Many times it will just verify the firmware is correct and can run the new iOS version, but not really change it.

It's just a step during update. The text for the user says "Installing", but that can mean many things. It does not necessarily mean its wiping it clean or anything. Just that it needs to set it up.

Why would you think that is wrong?

And what would it matter, if it wiped the firmware completely, and installed a clean one? There is no direct access to the firmware from a user or application standpoint, and the firmware changes don't affect your data.

It may or may not wipe it clean depending on what the update requires. No way to know as Apple does not publish these exact procedures for each update.

Why does it matter if it does or does not? You cannot change it, and it won't affect you either way?

In that case, there's no way to know what it does with 100% certainty. Again it may for some updates wipe it clean, it may not do so for others.

As said, to my knowledge Apple does not publish the exact steps every update takes. So no way to specifically say whether one update specifically wipes it or not each time.