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Is there a difference between updating iOS via OTA or iTunes? I have done some pretty good mucking around with my iPhone 4S's filesystem (e.g. deleting my Music folder). I have an inkling that the iTunes update is more thorough, and will reformat my entire filesystem, while I'm not so sure about the OTA update.

Does anyone have any in-depth knowledge they'd like to share on the matter?

Edit: I'll be going from 5.0.1 to 5.1.1

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You mentioned deleting your Music folder. Did you do that after JailBreaking, or did you just do it with a tool similar to i-funbox.com? –  Andrew Larsson May 23 '12 at 18:08
    
I think I did it with iExplorer. But I am jailbroken. Might have actually done it from Mobile Terminal. I forgot lol –  Thomas May 25 '12 at 16:34
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OTA updates do not work with JailBroken devices (even if you want to un-JailBreak your device). You should use iTunes. –  Andrew Larsson May 25 '12 at 17:51

4 Answers 4

up vote 8 down vote accepted

Yes at first approximation they are the same, but the mechanism of the update is different since one can be a delta and self-applied update and the other installs a complete build rather than patching the OS.

Digging deeper, the OTA update implies the OS and device is working properly, so iTunes is a good bet if you really want to ensure the update goes well or want to put the device into recovery mode to ensure the new OS and only the new OS is written. Obviously, if the device is having problems, you may opt for iTunes to control the update rather than hoping the device installs the patch properly.

Assuming your device is working well, you can safely update OTA and in many cases - the download is a delta update that is smaller than the entire image if you are doing an update that isn't a major version (4.0 or 5.0 which started the OTA capabilities and presumably 6.0 when it ships).

Using iTunes also gives you a chance to transfer purchases and reduce the number of apps you will have to re-download after a major update. Again, not an issue on incremental updates like 5.1.1 update from 5.1.

In practice, this even has been called out as a deciding factor for the jailbreak that was first released for iOS 7 where the notes said the exploit won't work against an OTA iOS 7 device, and only against a cleanly restored from iTunes device. I don't know if that has to do with the signing key or an actual difference in the two images, but it shows that the processes are indeed different in some respects.

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As @bmike notes, the processes are similar for OTA or iTunes. The OTA updates supply the deltas while the iTunes updates the whole build. The iTunes update also seems to run faster from my experience (purely anecdotal).

One big difference from my standpoint is the mandatory backup that occurs if you back up over iTunes - you can also transfer purchases and do any other management activities before the update. You can backup via Wifi with the OTA method as well, but that's a separate step that you'll need to explicitly kick off.

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If you use iCloud backup, you can backup to that, but at least my iPhone does it automatically every night, so backing up doesnt seem to be that much of an issue –  Jonathan. May 23 '12 at 19:12
    
@Jonathan., true, but not all users have set it up. Upgrading does entail a bit of risk, so the USB/iTunes way forces users to back up right before the update, whereas the OTA method leaves it up to the user to decide whether to back up before updating. –  JW8 May 23 '12 at 19:26

My understanding is that the update process is the same for both methods.

With the exceptions that iTunes downloads a several hundred megabyte IPSW file that can be used to do a more complete "restore" if needed. It is the "restore" that will reformat the filesystem etc.

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Thanks for the reply. That's kinda what I thought. I just wonder why iTunes doesn't just download the incremental update, instead of the entire IPSW. I'm gonna do a Reset All Setting from the handset and go from there lol. This is what happens when I'm in an experimental mood smh –  Thomas May 23 '12 at 16:11
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I'd say the end result is the same, but the two updates get there by pretty different paths. –  bmike May 23 '12 at 16:27

If you want to jailbreak later like for ios 7.1.4 or lower so update it on itunes not OTA

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Thanks for the reminder that this old thread is here. I updated my answer even though we originally were discussing iOS 5 jailbreaks. –  bmike Dec 29 '13 at 12:35

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