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Old Sep 24, 2009, 09:19 PM   #1
aerodoc
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Why "Erase all Content and Settings" so Quick?

I decided to try the "erase all content and settings" option to improve my GPS signal per Navigon FAQ. No problem, but after confirming the options, it seemed like it was only a minute or less before it asked me to just plug into iTunes.

I thought it was supposed to erase the data and I had about 18 gig of data so there is no way it could have done actually erased it in less than a minute. I have 3.1. Any idea why this sequence of events would occur? Has something changed in 3.1?

P.S. I remember talking to an Apple rep some time in the past about the erase all contents and settings and they said there is some kind of "encryption key" or something that if deleted could not be restored. I wonder if the just delete that key or something?
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Old Sep 24, 2009, 09:22 PM   #2
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I believe this is because since the data on the iPhone is hardware encrypted, the phone simply dumps the encryption keys.
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Old Sep 24, 2009, 09:23 PM   #3
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There's a reason it's called flash memory.....yes it can delete 18 gigs of data that fast in fact it should delete it faster. Now if the iPhone had a HDD then it would be a different story.
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Old Sep 24, 2009, 09:36 PM   #4
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Whether a device uses flash or rotating storage isn't the issue. Under normal circumstances, files aren't deleted by overwriting the data with zeroes. They're deleted by removing the file's entry in the file system. The size of the files isn't relevant, only the number of files matters. (In fact, the larger the average filesize, the less time it takes. 18 gigs of videos and music might only be ~1000 actual files. 18 gigs @ 10KB per file would take much more time to erase.)

Flash might help a little since it has excellent "seek" times, but it'd still be quite fast on a conventional disk.
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Old Sep 24, 2009, 10:15 PM   #5
aerodoc
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While I get what you guys are saying and understand all that, why is that if you search on "erase all content and settings" on this forum or on google, you will consistently find that it will take 2 hours or so (very rough number).

Navigon says about 2 hours here.
http://faq.navigon.com/opencms/inter...opicId_2=10714

This is the same statement made just about everywhere.
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Old Sep 24, 2009, 10:47 PM   #6
ElBerserko
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Quote:
Originally Posted by aerodoc View Post
While I get what you guys are saying and understand all that, why is that if you search on "erase all content and settings" on this forum or on google, you will consistently find that it will take 2 hours or so (very rough number).
Because the iPhone 2G and 3G are not hardware encrypted. They will take up to 2 hours because they write over all the data to keep it from being recoverable. With the 3GS, you just have to wipe over the encryption key which renders all the data on the device instantly unreadable. So 3GS will only take a second, older models will take an hour or two. The information on the internet is just referencing the facts about the older models.
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Old Sep 24, 2009, 11:11 PM   #7
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Great info. I did not realize this distinction, but it makes sense. When I did the same process on my 3G I remember it was quite slow. I suspected something like this, but did not (and still have not) actually seen a link that directly talks to it.
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Old Sep 24, 2009, 11:15 PM   #8
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I complain when people do that..
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Old Sep 25, 2009, 12:38 AM   #9
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Quote:
Originally Posted by ElBerserko View Post
Because the iPhone 2G and 3G are not hardware encrypted. They will take up to 2 hours because they write over all the data to keep it from being recoverable. With the 3GS, you just have to wipe over the encryption key which renders all the data on the device instantly unreadable. So 3GS will only take a second, older models will take an hour or two. The information on the internet is just referencing the facts about the older models.
I am curious how hardware encryption works. Does it mean the encryption routine is embedded in the ROM or something so the same OS-level write function can be used to write to both the encryption-enabed model (3GS) and the older ones (2G/3G)?
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