Firewire  -  IEEE 1394  -  iLink

Cable Length max = 4.5 meters, max daisy-chained devices = 17

Firewire, like USB, is a serial bus interface standard, offering high-speed data transfer between your computer and devices.  There are now two standards - the initial 400 Mbps IEEE 1394, and the subsequent 800 Mbps IEEE 1394b.  In May 2002, the IEEE standard 1394b was adopted, which describes transfer rates of 800 and 1,600 Mbps (S800 and S1600).  However, only the S800 speed has been adopted so far in the industry.

The History of Firewire

1. IEEE developed this standard and it was called IEEE 1394, with a data rate of 400 Mbps

2. Apple took up the protocol and named it "Firewire" - they used a 6-pin active connector

3. Sony took up the protocol and named it "iLink" - they used a 4-pin passive connector for devices

4. IEEE developed the next version, IEEE 1494b, with two data rates - 800 or 1600 Mbps

5. Since with IEEE 1394b there was now a "b" standard, the previous standard, formerly IEEE 1394 was renamed* to IEEE 1394a.  Similarly, Apple's initial "Firewire" was renamed* to "Firewire 400".
   
   * as with all tech name changes, they are not always followed.  Many vendors still use the original terminology !!  So whenever you see "Firewire" without the following 400 or 800, or "IEEE 1394" without the following "a" or "b" - you can safely assume they are referring to the first version.  In other words, Firewire = Firewire 400  and  1394 = 1394a

Because the name sounds cool, "Firewire" is what has stuck with most people and most vendors.

4-pin plug (Sony's iLink plug ) also called "Mini Firewire" for Firewire 400 active (self powered) devices no power is supplied through the cable - for devices such as Digital Camcorders	6-pin plug for Firewire 400 (IEEE 1394a) For computer ports and passive devices that require power 2 pins supply power	9-pin plug for Firewire 800 (IEEE 1394b) also called Firewire 2" For computer ports and devices (there is no active vs passive with 1394b).

4-to-6 Pin Cables - the Firewire port on your computer on-board 1394 port or on a 1394 PCI card
will likely be 6-pin, to support BOTH 4-pin and 4-pin firewire devices.  For example, your
device may be 4-pin and your PC port 6-pin.  In that case you need a 4-to-6 pin cable.

Daisy Chaining

Firewire Devices can be "Daisy-Chained" together.  However:

• they must have two Firewire ports on each device - one incoming and one outgoing (except for the last one, which only needs an incoming port)
• they will be sharing the bandwidth - for example, 3 drives on a Firewire 400 daisy chain, can only transfer a total combined data rate of 400 Gbps

Daisy-chaining hard drives is generally not recommended for Firewire 400.  However, with Firewire 800, you can get away with it - just make sure you use no more than 3 drives, and in reality you should probably use no more than 2 of them.

"Nodes" - how multiple daisy-chained Firewire Devices are addresses by your Computer

FireWire devices are organized on the bus in a tree topology. Each device has a unique self-id. One of the nodes is elected root node and always has the highest id. The self-ids are assigned during the self-id process that happens after each bus-reset. The order in which the self-ids are assigned is equivalent to traversing the tree in a depth-first, post-order manner.