Connectivity

Originally, a FireWire connection to the host computer was used to update songs or recharge the battery. The battery could also be charged with a power adapter that was included with the first four generations. The third generation began including a dock connector, allowing for FireWire or USB connectivity. This provided better compatibility with PCs, as most of them did not have FireWire ports at the time. The dock connector also brought opportunities to exchange data, sound and power with an iPod, which ultimately created a large market of accessories, manufactured by third parties such as Belkin and Griffin. The second generation iPod shuffle uses a single 3.5 mm jack which acts as both a headphone jack and a data port for the dock.
Eventually Apple began shipping iPods with USB cables instead of FireWire, although the latter was available separately. As of the first generation iPod nano and the fifth generation iPod classic, Apple discontinued using FireWire for data transfer and made a full transition to USB 2.0 in an attempt to reduce cost and form factor. With these changes, FireWire could only be used for recharging.

iPod Dock Connector
Introduced in the third-generation iPod, the iPod's 30-pin Dock Connector allows iPods to be connected to a variety of accessories, which can range from televisions to speaker systems. Some peripherals utilize their own interface, while others use the iPod's own screen for access. Such accessories may be used for music, video, and photo playback. Because the Dock Connector is a proprietary interface, the implementation of the interface requires paying royalties to Apple.[14][15]

Accessories