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You've probably read the USB Tekspek, and perhaps your intrigue, or product interest, has lead you to look up Firewire as well. The two are similar in some respects, particularly some of the products that use the two technologies. However, Firewire has its differences, which means it has both benefits and drawback when compared to USB. This Tekspek will look at Firewire and also look at it with respect to USB.
The first hurdle of Firewire is the name. It comes under many guises. Apple worked heavily on developing Firewire, and that's where the name came from. However, the IEEE (Institute of Electrical and Electronic Engineers) recognise it as standard 1394. You will, therefore, see the number 1394 used a lot to describe what you may otherwise know as Firewire. Sony also have their own implementation of Firewire. It's data-compatible with Firewire and is called iLink.
With all the names out of the way, how does it work? We'll start by focusing on the most common form of Firewire, which is the sort you'll likely need to be most familiar with. Firewire 400, as it is known (another name for you there) is a serial interface that allows data transfers of up to 400Mbits, along with the slower rates of 200Mbits and 100Mbits. 400Mbits equates to 50MiB/s.
A Firewire connector consists of either four or six pins. A six pin connector features a pin for power, one for ground and four pins for data, grouped into pairs. A six pin Firewire connector can provide or receive power of varying voltage at up to 45 Watts. The data is transmitted through a Firewire cable via twisted pairs of wire to reduce crosstalk and interference. A four pin connector doesn't have any power connections. Both connector types have a grounded shield around them, Firewire cables containing a 5 th (or 7 th ) wire to connect through this to ensure good shielding.
Firewire, unlike USB, allows daisy chaining of devices. That is, devices connected together in a chain can all communicate with each other, much like SCSI – the standard Firewire set out to replace, for external devices at least. Hubs can also be used, allowing up to 63 devices to be connected together.
Any Firewire device can, in theory, communicate with another, without the aid of a host. That means a computer doesn't need to 'oversee' the transfer of data between, say, a printer and a scanner, necessarily. Similarly, a chain of Firewire devices can have have more than one host, giving multiple hosts access to shared peripherals.
Like USB, Firewire is hot plug and play capable. However, the nature of the connectors and the higher power present on some of them, compared to USB, means that if a device is plugged into another while on, there is a chance of electricity arcing between pins. This has been known to cause short circuits which have subsequently killed Firewire controller chips. It is therefore not recommended to hot plug and play certain devices – DV camcorders, for example.
While USB 2.0 has a faster bit-rate than Firewire 400, it turns out that in some circumstances Firewire proves to be better. For one, Firewire tends to use less processor time when transactions are occurring. When data is transferred over Firewire, the two devices perform a handshake to prepare for the transfer, then the data is transmitted as one long stream. USB sends data as packets – breaking up the data into parts, with handshakes required for each packet. This makes Firewire better at sustained data throughput; ideal for multimedia solutions like scanners, DV cameras and other devices using high bandwidth streams of data.
You'll need one of these if you don't have Firewire on your motherboard.
A faster variant of Firewire, Firewire 800 is now also available. It is specified in the standard IEEE 1394b. It supports faster transfers (800Mbits or 100MiB/s), full duplex (data can be sent and received simultaneously), and has a newer 9-pin connector. A different type of encoding is used with Firewire 800 to cope with the increased rate at which signaling is occurring over the cables.
Networking is also supported over Firewire. A Firewire device have a MAC address associated with it, and the likes of Windows, Mac OS and Linux support TCP/IP over Firewire, allowing small Firewire networks be constructed.
In the technology section of this Tekspek we established the type of device to which Firewire is best suited. So, we have a great many DV camcorders out in the market, all supporting Firewire. Many scanners also support it.
External storage also exists with Firewire support. In fact some external storage devices feature both USB and Firewire interfaces. As we've already established, Firewire's quicker at sustained transfers, but if you're dealing with a large number of smaller files, then USB 2.0 may prove the quicker of the two technologies. Of course, buying a device with both interfaces allows you to test both out, and find out which is best for you, providing the thing you're connecting the device up to also has the two interfaces.
Apple has, as you'd expect, made good use of Firewire for its external devices. The venerable iPod uses the Firewire interface. However, newer models feature USB 2.0 and Firewire. In fact, the latest models no longer have Firewire, and indeed some of Apple's newest computers don't have Firewire on them any more. Perhaps the biggest reason for this is that the iPod is popular with PC users too, and given all PCs and Apple Macs feature USB, sticking with the single interface is easier.
Firewire, including its newer forms, will continue to be used for multimedia devices, so don't expect it to disappear any time soon. However, it is certainly more commonly used by professionals working in media than by regular consumers these days.
It goes without saying that Apple is one of the key players in Firewire. They did much of the development and their support for Firewire brought it to where it is today.
Other companies involved in Firewire include Sony (with their iLink brand of Firewire) along with other DV camera manufacturers. For storage devices, Prolific and Oxford are the two most common chips found in external drive enclosures requiring and IDE (hard drive interface) to Firewire bridge, but their chips are usually encompassed within other products.