How to Downgrade Your iPhone 3G[S] from iOS 4 to iOS 3.1.3（情報元のブックマーク数）
iPhone 3GをiOS3.1.3に戻す方法
A lot of iPhone 3G owners myself included have discovered that upgrading to iOS 4 has slowed their devices to a crawl. If you decide the new features and shortcuts just aren't worth the glacial performance, here's how to downgrade your iDevice.
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Note: The process should work nearly the same on Windows and OS X, so unless we say otherwise, you can follow the same steps on each. The main difference between Windows and OS X is RecBoot, so Windows users, make sure you pay close attention to the RecBoot process before diving in. The same basic steps should likely work for iPhone 3GS, according to our 3GS-toting intern Adam Dachis, who's used a similar method in the past. (Still, I haven't been able to verify, so proceed at your own risk, and if you do, let us know how it worked in the comments.) Lastly, you should read through the entire guide before you dive in, just so you know what you're getting into. Image remixed from drewm.
3.1.3のイメージがのこっていれば可能みたい。
restore-os.jpgThe first thing you need to do is get a copy of the iPhone OS 3.1.3 image. There's a good chance you've already got a backed up copy of the 3.1.3 release on your system, so let's check there first. On OS X, check in ~/Library/iTunes/iPhone Software Updates. On Windows, your iPhone OS updates should be stored in C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPhone Software Updates (or to get there more quickly, type Win+R and paste %appdata%\Apple Computer\iTunes\iPhone Software Updates). If you see a file inside this folder corresponding to iPhone1,1_3.1.3_7E18_Restore.ipsw or iPhone1,2_3.1.3_7E18_Restore.ipsw, those are likely the restore images you need.
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