IEEE 1394

IEEE 1394 (also known by Sony's iLink, Apple Computer's FireWire brand names and DV port) is a 1995 personal computer and digital video serial bus interface standard offering high-speed communications and isochronous real-time data services, developed primarily by Apple Computer. It is defined in IEEE 1394.

The system is commonly used for connection of data storage devices and digital video cameras. It is used instead of the more common USB due to its faster speed, and because it does not need a computer host. It also does not need to send a signal telling the other component that it is "alive": a data interruption that makes USB ineffective for professional video work. However, the small royalty that Apple has demanded from users of FireWire and the more expensive hardware needed to implement it has prevented FireWire from displacing USB in low-end mass-market computer peripherals where cost of product is a major constraint.

It can daisy-chain together up to 63 peripherals in a tree-like structure (as opposed to SCSI's linear structure). It allows peer-to-peer device communication, such as communication between a scanner and a printer, to take place without using system memory or the CPU. It is designed to support plug-and-play and hot swapping. Its six-wire cable is not only more convenient than SCSI cables but can supply up to 60 watts of power, allowing low-consumption devices to operate without a separate power cord.

FireWire 400, tracking the IEEE 1394a specification, can transfer data between devices at 100, 200, or 400 Mbit/s with four or six-pin cables. Cable length is limited to 4.5 meters but up to 16 cables can be daisy-chained yielding a total length of 72 metres under the specification.

FireWire 800, which tracks the IEEE1394b standard and was introduced commercially by Apple in 2003, allows an increase to 800 Mbit/s (Mbps) with a nine-pin cable. Due to the professional grade optical fibers used in the Firewire 800, it is only limited to 100 meters in length It does not have the cable-length limitation of FireWire 400. Further speed increases to 2 Gbit/s are planned. Other than the original FireWire 400 standard which used a data/strobe (D/S) encoding (called legacy mode) on the signal wires, FireWire 800 uses a data encoding scheme called 8B10B (also referred to as beta mode).

Some expensive camcorders have included this bus since 1995. All Macintosh computers currently produced have built-in FireWire ports. With this new technology, FireWire, which was arguably already slightly faster, is now substantially faster than USB 2.0. FireWire is also used on the iPod music player, permitting new MP3 tracks to be downloaded in a few seconds.

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Based on material from FOLDOC, used with permission. IEEE

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