Apple today launched the new version of its iTunes software for Mac and Windows PCs. The new software is available as a free download and will be installed automatically provided users allow the automatic update feature to function normally.

In The Hypervisor tests the first thing that most people noticed was the Snow Leopard style facelift that has been applied to the iTunes user interface. iTunes also gets some exciting new synchronization capabilities. For example, iTunes can now sync with five devices, which could be PCs, iPhones or iPods. For people with iTunes installed on multiple computers this makes it much easier to maintain a synchronized copy of their iTunes library on each PC.

There’s also been a few useful changes to how iTunes synchronizes with iPhones and iPods. Given that most people have much more data in their iTunes library than they could fit in their iPhone or iPod, many people need to select a subset of their library to be synchronized with their mobile devices. Previously iTunes allowed only selected Playlists to be synchronized. Now users can select individual artists and genres to synchronize too. There are also options to control whether music videos and voice notes are synchronized, and an option to automatically fill free space with music.

iTunes 9 can also be configured to synchronize Calendar, Contacts, Notes and email accounts with software running on your PC. However, there’s not much change here from previous versions – as before, the main limitation is that information is only synchronised when the iPhone is connected to the PC – either by USB cable or Bluetooth. There’s also a nice option to encrypt iPhone backups, which would be particularly useful for people that use iTunes on an office computer.

One potential hiccup of the upgrade is that after the first sync between iPhone and iTunes 9, iTunes will ask the user to reauthorize their iPhone. If they decline to do this all their apps and songs from the iTunes store will be deleted.