Turn Your IPod or IPhone Into a Portable Drive
latimes.com
Enable your iPod
You can turn any iPod (except iPod touch, see below) into a portable drive using iTunes. If you manually manage your music instead of having iTunes automatically sync songs, you don't need to do anything-your iPod is already set to function as an external drive, and will mount and be accessible on your desktop whenever you connect it.
If you set iTunes to automatically sync music to your iPod, you'll need to enable disk use; connect your iPod to your Mac, open iTunes, and select your iPod in the Source pane under Devices. Click the Summary tab (or Settings tab for iPod shuffle) and then select the "Enable disk use" checkbox. Your iPod will now mount as a drive volume on your desktop whenever you connect it.
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