The History of Firewire
Firewire, IEEE 1394, is a personal computer and digital video serial bus interface
standard offering high speed communications and isochronous real time data services,
developed primarily by Apple Computer, completing development in 1995. It is defined
in IEEE standard 1394 which is currently a composite of three documents: the original
IEEE Std 1394-1995, the IEEE Std 1394a-2000 amendment, and the IEEE Std 1394b-2002
amendment. Sony implementation of the system is known as i.Link, and uses only
the four signal pins, discarding the two pins that provide power to the device
in favour of a separate power connector on Sony i.Link products.
The system is commonly used for connection of data storage devices and digital
video cameras, but is also popular in industrial systems for machine vision and
professional audio systems. It is used instead of the more common USB due to its
faster speed, higher power distribution capabilities, and because it does not
need a computer host. It also has native support for isochronous data transport,
data that must be delivered with deterministic latency, such as audio or video.
However, the small royalty that Apple Computer and other patent holders has initially
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 connect together up to 63 peripherals in a non-cyclic network structure,
as opposed to SCSIs 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. Firewire also supports multiple hosts per bus, and through
software IP networks can be formed between Firewire-linked computers. 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 45 watts of power per port, allowing
moderate-consumption devices to operate without a separate power cord. Note: that
the Sony inspired iLink usually deletes the power part of the cable, connector
system and only uses a 4 pin connector.
Firewire 400 can transfer data between devices at 100, 200, or 400 Mbit/s data
rates, actually 98.304, 196.608, or 393.216 Mbit/s, but commonly referred to as
S100, S200, and S400. Cable length is limited to 4.5 metres but up to 16 cables
can be daisy chained yielding a total length of 72 meters under the specification.
Firewire 800, Apples name for the 9 pin "S800 bilingual" version
of the IEEE1394b standard, was introduced commercially by Apple in 2003, and allows
an increase to 786.432 Mbit/s with backwards compatibility to the slower rates
and 6 pin connectors of Firewire 400.
The full IEEE 1394b specification supports optical connections up to 100 metres
in length and data rates up to 3.2 Gbit/s. Standard category 5 unshielded twisted
pair supports 100 metres at S100, and the new p1394c technology goes all the way
to S800. The original 1394 and 1394a standards used data/strobe, D/S, encoding,
called legacy mode, on the signal wires, while 1394b adds a data encoding scheme
called 8B10B, also referred to as beta mode. With this new technology, Firewire,
which was arguably already slightly faster, is now substantially faster than USB
2.0.
Almost all modern digital camcorders have included this connection since 1995.
All Macintosh computers currently produced have built-in Firewire ports, as do
all Sony PCs and many PCs intended for home or professional audio/video use. Firewire
is also used on the iPod music player, permitting new tracks to be uploaded in
a few seconds and also for the battery to be recharged concurrently with one cable.
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