how do i backup my ipod classic 80GB model A1238 to itunes (I manually manage syncing)

The backup function in iTunes is only for iOS devices (iPod touch, iPhone, and iPad). Media player iPods are synced from your iTunes library. All of its content came from your iTunes library, so it's already "backed up" in your iTunes library. What you need to back up is your iTunes library on your computer, in case your computer or its drive fails.

In case what you really want to do is copy the media off the iPod see Recover your iTunes library from your iPod or iOS device. For advice on backing up your library see Backup your iTunes for Windows library with SyncToy.

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