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 metres 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 with a
nine-pin cable. 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.