What is Firewire?

The IEEE 1394 interface, commonly known as FireWire, is a standardized high-speed serial bus interface capable of isochronous (same time) data transfer. Developed largely by Apple in 1995, the original FireWire standard is capable of data transfer speeds up to 400 Mbps. FireWire also supports multiple hosts per controller bus, computer-independent peer-to-peer communication (I.e., scanner to printer), and “hot-swap” and plug-and-play. FireWire networks can support up to 63 peripherals in a tree topology. FireWire is intended by Apple to both replace the legacy SCSI interface—mainly providing external hard drive and optical drive connectivity—and provide a new connectivity standard for audio and video. Like USB, it is mainly used to provide interfacing of computer peripherals and devices. 

Two additional FireWire specifications, IEEE 1394a and 1394b, were released in 2000 and 2002, respectively. 1394a implemented asynchronous data streaming, a power-saving suspend mode, and standardized a 4-pin FireWire connector; the 4-pin is fully compatible with regular 6-pin adapters, but does not draw any power. 4-pin connectors are typically found on laptops, consumer camcorders, and other “mobile” FireWire devices. The new 1394b standard supports data speeds up to 800 Mbps via a new encoding system called beta mode. Although 1394b is backward-compatible with 1394a, the 1394b connector is an entirely new 9-pin design, thus rendering old cables incompatible with the new standard. 1394b also provides support for new 1600 Mbps and 3200 Mbps variants; products capable of these speeds should be available by the end of this year (2008).

Compatibility

FireWire is fully supported by several variants of Linux and Apple's Mac OS X. Microsoft's Windows XP, as of SP2, only supported data speeds of 100 Mbps, even for FireWire 400 and 800 devices.

Practical Data

• In addition to the traditional serial cable, FireWire is available in wireless, fiber optic, and coaxial forms; all utilize isochronous protocols.
• The maximum length of a FireWire cable is 4.5 meters (15 feet). Like USB, practical use of a cable longer than 4.5m diminishes as signal delay increases.
• Similar to USB extension schemes, a single FireWire cable can be extended to 25m (80 feet), using either five daisy-chained hubs or five 4.5m extension cables with internal hubs.

FireWire and USB

FireWire and USB are both serial interfaces designed mainly for computer-to-peripheral/device connections, but the minor technical differences between the two standards favor different applications for each. FireWire's ability to sustain greater rates of data transfer than USB, combined with its power-distribution properties, make it a favorite of professional videographers, A/V enthusiasts, and high-speed data storage devices and drives. FireWire's higher hardware cost per device, however, makes it less practical than USB for everyday peripheral and device applications. Low-cost, mass-production peripherals like keyboards, mice, and flash drives would be economically impractical if FireWire were used instead of USB.