iTunes 10 for Mac: Use Autofill to add content to iPod, iPhone, or iPad
iTunes can quickly fill your device with random songs from your library. You can use Autofill to fill up your entire device, or you can use it after you sync your device manually to fill remaining space.
Autofill is available only if you manage the music on your device manually. Connect your device to your computer and make sure “Manually manage music” is selected in the Summary pane in iTunes.
To use Autofill:
Connect your iPod, iPhone, or iPad to your computer.
In iTunes, select Music (below your iPod, iPhone, or iPad in the list of devices). The controls for Autofill appear at the bottom of the Music pane:
Click Settings to see the Autofill Settings window:
When you’re done selecting your options, click OK.
To fill your device, click Autofill.
iTunes saves your settings until you change them. Each time you use Autofill, it adds different songs to your device, even if you don’t change your settings.