Apple introduced the third generation iPod on April 28, 2003. Unlike earlier iPods, the 3G iPod no longer had button surrounding the scrollwheel. Intead, there were four control buttons located between the scrollwheel and the screen.
The new iPods were more energy efficient than older ones and managed 8 hours of play time with a 630 mAh battery, trading off some play time for a smaller battery. This allowed Apple to make the 3G iPods thinner and lighter.
The other big change was elimination of the FireWire port in favor of a dock connector on the bottom of the iPod. This made it easy to plug the iPod into a dock for charging and synching. The dock connector also made it possible to use the new iPods with either FireWire or USB.
Apple no longer produced different models for Macs and Windows.
The 15 GB and 30 GB models were replaced by 20 GB and 40 GB ones in Sept. 2003. The 10 GB model was discontinued and replaced by a new 15 GB model in January 2004.