The anatomy of Firewire

Why on earth would one want to dissect a Firewire card ? After all , all these cards are the same right ? I mean PCI in Firewire out ? no ? .... No! Unfortunately that is not so. There are slight differences between the cards that are out there. Some might be obvious , like the number of ports , but some are much less obvious. And some are even hard to spot unless you are an electronics engineer who eats electrons for breakfast everyday. So it's time for a little Show and tell ... about Firewire and everything related to it.

Firewire: Past , present and future..

The name Firewire was coined by a group of Apple engineers in or around 1986. Adaptec, the leading supplier of computer I/O peripherals, was one of the first companies with a 1394 Firewire board shipping in volume. In 1995 it was officially embraced by the IEEE ( Institute of electrical and electronics engineers , pronounced I-Triple-E) and labeled as the IEEE 1394 standard. A number of IEEE 1394 products are now available including digital camcorders with the IEEE 1394 link. The Digital VCR Consortium (consisting of more than 50 manufacturers of consumer electronics firms) adopted the IEEE1394 High Performance Serial Bus as the standard digital interface between consumer DV products.

The current standard known as IEEE1394-1995 ( for the year it was accepted ) is very closely guarded and any manufacturer building a product that wants to be IEEE1394 has to comply to the standard and pay royalties. 0.25 $ per device manufactured goes to the owner of the standard : Apple Computers.

The strong multimedia orientation, versatility and high performance of 1394 have encouraged new concepts soon to be released or in development now. With the native IEEE 1394 support in Microsoft Windows operating systems, a number of new applications for 1394 will come forth that bridge consumer and computer electronics.

A pending review of the standard will boost the speed of the bus even further.

Firewire technicalities:

Firewire as we know it ( IEEE1394-1995 ) can transfer data between devices at 100, 200, or 400 Mbps. It is designed to support plug-and-play and hot swapping. The six-wire cable can supply up to 60 watts of power, allowing some devices to operate without a separate power cord. For device not requiring external power there is the 4 pin plug that carries the same data channels but omits the power. Each cable carries 2 channels. One up-link and one downlink. To reduce crosstalk and noise the signals are transmitted differentially ( there is no ground. ) Basically what happens is a polarity reversal on the cable. Error correction codes in the stream reduce the susceptibility to noise even further. Firewire cables can be pretty long ( up to 17 meters without ).

Firewire as it is can daisy-chain together up to 63 peripherals in a treelike structure You can connect the devices any way you want . Its big difference with USB and USB2.0 is that 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. USB is a single master bus, the computer is always in control , where as on Firewire multiple computers can be talking to multiple devices on the same bus. Firewire is much more like a computer network then a simple point to point connection. It is perfectly possible for the camera (1) to stream data to the PC (1) , while at the same time the CD writer (2) is recording data from drive (2). Yet another process can be Delivering data from the raid storage (3) to another camera (3). all of this happens while two PC's (4) are exchanging files.

On USB the above would be impossible. For starters you can't have multiple PC's , so even if you could hook up all the storage devices and the two camera's it would be impossible for camera 3 to get data from the drive , while the PC is reading data from camera 1. Simple reason : the camera that requires data has to request it from the PC , that in turn gets it form the drive. On Firewire the camera can request data from the harddisk directly. There are DV camera's that can exchange data with a harddisk . The PC has to create the file and open it but once the file is open the PC instructs the camera to redirect its output stream directly to the disc. When the camera is done it notifies the computer that then closes the file.

The computer to computer link can run TCP/IP protocols and act as a very fast network ( 400 Mbit/s ) . Another scenario is to open the RAID storage form multiple computers at the same tame thus instantly creating a shared drive.