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USB and Firewire confusion


© December 2005 Tony Lawrence

New Macs of course support USB. Unfortunately, there is the original, low speed USB (1.5 Mbs) and "Full Speed" (12 Mbs). As "High Speed" USB 2.0 is 480 Mbs, that "Full Speed" is a bit misleading.

If you have a new Mac, you have the full 480 Mbs capability. You also have Firewire, which is either 400 Mbs or (newer) 800 Mbs. Firewire has another advantage in being able to provide more power over the bus; 30V vs. USB's 5V. External storage may be USB or Firewire, and the market is constantly shifting.

When buying devices, whether Firewire or USB, watch for labeling to be sure you are getting what you want. As noted above, "Full Speed USB" sounds great, but it's actually very slow. A "Firewire" device is probably the 400 Mbs type unless it specifically says otherwise. Currently, for example, iBooks have only 400 Mbs Firewire while the Power Mac G5 has both 400 and 800.

It can be pretty confusing, and "system_profiler" doesn't help: it will tell you the maximum speed of your Firewire bus, but not of the USB. External devices may not be explicit about speeds either, so you really have to read carefully and check in depth when necessary.


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