The copper wire can extend up to 4.5 meters (15 feet) and was replaced by Thunderbolt in newer Macintosh models.
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony and Panasonic. It is most commonly known by the name FireWire (Apple), though other brand names exist such as i.LINK (Sony), and Lynx (Texas Instruments).
The copper cable used in its most common implementation can be up to 4.5 metres (15 ft) long. Power and data is carried over this cable, allowing devices with moderate power requirements to operate without a separate power supply. FireWire is also available in Cat 5 and optical fiber versions.
The 1394 interface is comparable to USB. USB was developed subsequently and gained much greater market share. USB requires a host controller whereas IEEE 1394 is cooperatively managed by the connected devices.