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You needed iTunes to act as a conduit to get songs onto the iPod, but you could either sync it with one iTunes library, or leave it in manual mode and load songs from any iTunes.

It worked then exactly the same way as it does now[1].

You couldn't sync songs on the device back into iTunes though[2] - if you had it in manual, put some songs on it (from another iTunes library, a third party app or anywhere else) and then tried to sync it with your iTunes, it would remove everything on there before syncing over your iTunes library.

1: http://support.apple.com/en-us/HT201593 2: Without one of many third-party helper apps. Sentuti was a lifesaver!