The main types of ports in a PMP are the audio-out ports, which are used to pipe music to speakers or headphones. Some PMPs offer a TV-out port, which lets you hook it up to a large screen. USB and Mini USB ports are standard offerings for transferring media, along with power ports. iPods have a FireWire port, which allows simultaneous charging and data transfer. The FireWire port can also be used to attach to external speakers and the ubiquitous iPod dock.