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FireWire allows for faster data transfer between high-bandwidth devices like digital camcorders, surpassing USB speeds. Image courtesy of Ross M. Horowitz / Getty ImagesYou might have come across the term FireWire if you're into digital video, or perhaps you recognize it as Sony's i.Link or by its official name, IEEE 1394. FireWire enables seamless and rapid data sharing between different devices.
Initially developed by Apple and standardized in 1995 as IEEE 1394 High Performance Serial Bus, FireWire shares similarities with Universal Serial Bus (USB). The engineers who created FireWire had a few specific objectives in mind while designing the standard:
- Rapid data transfer
- Capability to connect numerous devices to the bus
- User-friendly interface
- Hot-pluggable functionality
- Power delivery through the cable
- Plug-and-play compatibility
- Affordable cabling costs
- Low implementation expenses
In this article, we will explore what FireWire is, how it functions, and why you might find it useful.
What is FireWire?
FireWire 400 connectorsFireWire is a technology for transferring data between digital devices, particularly in the audio and video domains. Also referred to as IEEE 1394, FireWire boasts impressive speed, with the latest version reaching 800 Mbps. In the future, that speed is anticipated to soar to an extraordinary 3.2 Gbps when updates to the FireWire cables are made by manufacturers.
You can connect as many as 63 devices to a FireWire bus. Both Windows (98 and newer) and Mac OS (8.6 and newer) support this technology.
Imagine connecting your digital camcorder to your home computer. When you turn on your computer, it queries all connected devices on the bus and assigns each one an address in a process called enumeration. FireWire is plug-and-play, so when you add a new FireWire device, your operating system automatically detects it and prompts you for the driver disc. If the device is already installed, your computer activates it and begins communication. FireWire devices are hot pluggable, meaning they can be connected and disconnected at any time, even while powered on.
Now, let's dive into the details of FireWire's specifications.
FireWire Specifications
The original FireWire specification, FireWire 400 (1394a), was faster than USB when it first launched. FireWire 400 is still widely used today and offers the following features:
- Transfer speeds of up to 400 Mbps
- Maximum device distance of 4.5 meters (cable length)
When USB 2.0 was released, offering transfer speeds up to 480 Mbps and distances of up to 5 meters between devices, it narrowed the gap between the two standards. However, in 2002, FireWire 800 (1394b) began appearing in consumer products, leaving USB 2.0 behind. FireWire 800 is capable of:
- Transfer speeds up to 800 Mbps
- Maximum device distance of 100 meters (cable length)
The faster 1394b standard is backward-compatible with 1394a.
In the following section, we'll dive deeper into the FireWire vs. USB discussion.
FireWire vs. USB
The main distinction between FireWire and USB lies in their intended use: FireWire is designed for devices that handle large amounts of data, such as camcorders, DVD players, and digital audio devices. While FireWire and USB share similarities, they also differ in key areas.
Implementing FireWire is slightly more expensive than USB, which is why USB has become the go-to standard for connecting most peripherals that don't require high-speed data transfer.
Aside from speed, the major difference between FireWire and USB 2.0 is that USB 2.0 is host-based, meaning devices must connect to a computer to communicate. On the other hand, FireWire is peer-to-peer, so two FireWire cameras can communicate directly with each other without the need for a computer.
Now, let's revisit how FireWire is implemented. How do you make the connection?
FireWire Cables and Connectors
FireWire devices can be either powered or unpowered. FireWire allows connected devices to draw power directly from the connection. The cable has two power conductors capable of supplying power (ranging from 8 to 30 volts, with a maximum of 1.5 amps) from the computer to an unpowered device. The data is carried over two twisted pair sets in a FireWire 400 cable, using a 6-pin configuration.
FireWire adapter cable (9-pin configuration on the left)
Photo courtesy HSW ShopperSome smaller FireWire-enabled devices utilize 4-pin connectors to save space, eliminating the two pins typically used for power supply.
FireWire 800 cables are designed with a 9-pin configuration. Six of these pins are identical to the six pins in the 1394a connector (shown earlier). Two of the additional pins create a "grounded shield" to prevent interference with the other wires, while the third extra pin is currently unused [ref].
Since FireWire 800 is backward-compatible with FireWire 400, there are multiple adapters that allow both standards to work together on the same bus. Additionally, there are two types of FireWire 800 ports: a "bilingual" port that accommodates both FireWire 400 and 800 standards, and a b-only port that accepts only FireWire 800 connectors.
Sending Data via FireWire
FireWire utilizes 64-bit fixed addressing as per the IEEE 1212 standard. Each packet of data sent through FireWire contains three key components:
- A 10-bit bus ID that identifies which FireWire bus the data originates from
- A 6-bit physical ID that determines which device on the bus sent the data
- A 48-bit storage area capable of addressing up to 256 terabytes of data per node
The bus ID and physical ID together form the 16-bit node ID, which allows for up to 64,000 nodes in a system. Data can travel across a maximum of 16 hops (device-to-device). Hops happen when devices are daisy-chained together. In the example below, the camcorder is connected to an external hard drive, which is connected to Computer A. Computer A is linked to Computer B, and Computer B connects to Computer C. In this scenario, it takes four hops for Computer C to access the camcorder.
If all the devices in this setup support FireWire 800, the camcorder can be positioned as far as 400 meters away from Computer C.
Now that we've explored how FireWire operates, let's dive deeper into one of its most widely used applications: streaming digital video.
FireWire and Digital Video
FireWire truly excels in digital video applications. Nowadays, most digital video cameras or camcorders are equipped with a FireWire port. Connecting a camcorder to a computer via FireWire provides an impressive experience.
A key feature of FireWire is its support for isochronous devices. In isochronous mode, data flows in real-time between the device and the host with a guaranteed bandwidth and no error correction. In simple terms, this allows a device like a digital camcorder to request sufficient bandwidth from the host computer to transmit uncompressed video in real-time. When the connection between the computer and the camera switches to isochronous mode, the camera can send video to the computer in a smooth, uninterrupted flow.
Editing and creating custom video projects is a breeze when you have fast hard drives, a digital camcorder, and a computer. With the appropriate software, the computer and camcorder work together seamlessly, allowing the computer to download the video effortlessly, maintaining perfect digital clarity. Since the content remains digital throughout the entire process, there is no loss in quality even after multiple generations of editing.
