A FireWire® cable is useful for moving files from one device to another, and, as of September 2011, there are two speeds: 400 and 800. The number represents FireWire® speed in megabits per second (Mbit/s). In terms of pure speed, the FireWire® 800 is obviously better, but there are instances in which the 400 is better. If the computer is weak or slow, then the better FireWire® speed may not be useful, because the computer cannot support the data flow. Some people may worry about the compatibility between the 400 and 800, but this issue is not as important as most users believe; depending on the common files that are transferred, getting the faster FireWire® speed may not save users much time.
The easiest factor to determine between the two FireWire® cables is their speed. FireWire® 400 is capable of moving files at 400 Mbit/s, while the FireWire® 800 is capable of transfer speeds of 800 Mbit/s. In this arena, the 800 FireWire® speed is obviously better, but there are conditions that can prevent this faster wire from working at full capacity.
Depending on the device or computer to which the FireWire® is attached, the wire may not be able to sustain its optimal speed. New and modern computers, or those with powerful drive technology, can easily sustain the FireWire® 800 transfer rate. Older computers have trouble sustaining this speed, and the 800 FireWire® speed may slow down, on average, to around 550 Mbit/s, which is not much better than the FireWire® 400. If the computer or device is old or slow, then the FireWire® 400 will deliver about the same performance as the 800 at a lower cost.
Compatibility is an issue with many computer parts, simply because parts that are not compatible will not transfer data or work. This is not an issue in choosing a FireWire® speed, because both the 400 and 800 are backward- and forward-compatible. A 400 device can work with an 800 wire, and an 800 device can work with a 400 wire.
Users should check the files they commonly transfer to see which FireWire® speed would be best. If users transfer entire hard drives or gigabytes (GB) of data, then the FireWire® 800 will be useful in decreasing transfer times. Small file transfers will not receive the same benefit. For example, if 1 megabyte (MB) of data is transferred on average, then using the FireWire® 800 will save less than a second, which may not be worth the extra expense.