Questions about reverting to 9.3.5

[Smoothie]

Before updating my iPhone 6 to iOS 10 via iTunes, I manually saved a backup of 9.3.5 to iTunes on my MBP. When iOS 10 installed, the installation process also seemed to create a backup before starting the installation process. When I go into iTunes to check my backups, I only see one backup from the day I installed iOS 10, so it appears that the installation process overwrote my earlier backup.

Does the backup when done from iTunes back up the prior OS version or does it simply back up apps, data and settings? Can I assume that the one backup shown in iTunes is the 9.3.5 installation? Can I simply restore from this backup to get 9.3.5 back or do I need to download the iOS 9.3.5 version from Apple, assuming it's still available, and then restore from iTunes to get my apps, data and settings back?

I've never reverted to an earlier Apple OS before, but iOS 10 is causing problems on my iPhone 6.

 

[newellj]

Backups do not backup the firmware/OS, only apps, data and settings.

If you don't/didn't archive the 9.3.5 backup, a subsequent 10.0.1 backup will overwrite it, so the later backup is probably not your 9.3.5 backup.

You can't restore a 10.0.1 backup to a phone running 9.3.5.

You can archive a backup by going to iTUnes>Preferences>Devices and right-clicking the backup you want to archive and selecting "archive."

If you hover of the list of backups on the "Devices" page/tab, it will show you the version of iOS that was installed when the backup was made.

If you want to revert to 9.3.5, you need to Google up the .ipsw file and then download the file, then do an alternate key (I think it's "option" but it may be the "control" or "command" key - you can Google that also) in iTunes to restore the older firmware, assuming it's still being signed by Apple.

If you don't have a good 9.3.5 backup, though, you'll have to rebuild the phone from scratch.

 

[Smoothie]

Thanks for the reply. While I was away from this forum, I successfully reverted to 9.3.5. It took awhile, but everything seems to be as it was before I updated to iOS 10. The backup that the iOS 10 install created after I had already backed up must have been based upon state of the phone under iOS 9.3.5 since the reversion worked. (Either that or it didn't overwrite my backup.) I had to rescan my fingerprints, but most other settings are as they were. I'll wait until Apple releases a few updates to iOS 10 before considering trying again. Although, by then there'll probably be no way to revert.

Your post will help others who may be thinking of reverting.