OTA Updates

OTA Updates (Over-the-Air Updates, also know as wireless updates) were introduced with iOS 5. This allows a user of a device to go into Settings > General > Software Update and download and install the latest iOS software on-device, without the need for iTunes. The device contacts mesu.apple.com to check for updates. The updates are delivered in plain unencrypted ZIP files.

Issues with jailbreaking

 * OTA Updates are often known to cause issues when jailbreaking a device. This became evident with evasi0n7, because most devices that were updated OTA, had to be restored with iTunes first, since the jailbreak would often fail if it was not.
 * You cannot update OTA, when jailbroken. If you try, it is likely that your device will either be stuck in a boot loop, or certain things will not work correctly. Newer jailbreaks such as evasi0n and evasi0n7 disable the OTA search daemon, which prevents the device from searching for an update (it will just stay indefinitely at "Checking for Update..."). This can also be done manually on any jailbreak, by deleting or moving /System/Library/LaunchDaemons/com.apple.mobile.softwareupdated.plist and /System/Library/LaunchDaemons/com.apple.softwareupdateservicesd.plist from your device. It can also be done with tools such as iCleaner Pro.

Going from 5.0.x to 6.1.3
On iPad 2, iPhone 4s and iPhone 5, any users on iOS 5.0 or 5.0.1 must go to 6.1.3 via OTA before they can find and install an OTA update for 8.x. This is not a mistake, but was planned to keep the amount of OTA files down.

Apple TV
NOTE: "Marketing Version" is the version that the Apple TV reports in its "About" screen.