Announced by Apple in 1995, FireWire was used for high-speed data transfers and for downloading digital video direct from FireWire-equipped camcorders. With a transmission rate of 400M bit/sec., FireWire handily outsped USB 1.1's 12M bit/sec. maximum throughput and gave it a real advantage where speed was essential, such as in moving large graphics files. Another advantage to FireWire is that it doesn't need a computer host, nor does it need to signal the other component that it's "alive," as current USB implementations must. This kind of data interruption makes USB impractical for most professional video work.
However, Apple gets a small royalty for each product that uses Firewire, and FireWire is more expensive to implement. These two factors have prevented FireWire from supplanting USB in low-end computer peripherals, where cost is critical.
Like USB, Firewire can daisy-chain peripherals together (up to 63, in a treelike structure), and it delivers up to 60 watts of power to peripherals. Firewire allows peer-to-peer device communications and allows hot-plugging and -unplugging. Cable length is limited to 4.5 meters between devices.
With USB 2.0, FireWire has been leapfrogged. However, a higher-speed release of FireWire is expected to up the ante again, providing speeds of up to 2G bit/sec.