Apple released i OS 6.1.5 on November 14, 2013, to fix a bug for the fourth-generation i Pod.
Only the fifth-generation i Pod Touch, the most recent version at of time of publication, is able to support i OS 7.
All i Pad models except the original can be updated to i OS 7, and i Phones from the i Phone 4 onward are supported as well.
Personally, I prefer to manually sync my music and media, so I have all of the individual content sync features disabled and sync everything myself through drag & drop.
If syncing fails, the Sync button is greyed out and not available at all, or if you try to sync and nothing transfers over to the i Phone, i Pod, or i Pad, you may simply need to authorize the computer with i Tunes: This is a surprisingly common problem and it’s extremely easy to resolve.
According to Apple’s Support Communities, i OS 7 requires at least 512MB of memory.
The fourth-generation i Pod has only 256MB of memory, so it cannot support the upgrade to i OS 7.
If you find yourself in that frustrating situation, here is what you can do to fix it and get the i Phone, i Pod, or i Pad syncing with i Tunes on a Mac or PC again.
We’re going to cover a variety of troubleshooting tricks to fix the syncing problem here, try each in descending order until the problem is resolved.
If you try to download an app from the i Tunes App Store that is not supported by your current i OS version, a message asks if you would like to download an older version of the app.
Apple is able to direct your device to the most recent compatible app version, reaching as far back as i OS 4 versions.
The i OS 6.1.5 release was issued to correct errors that caused Face Time video calls to fail.