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I'm about to purchase an iMac and I'm looking to get a large 1-2TB external hard drive to work with the iMac backup software (Time Capsule) as well as to store music and photos.

I'm curious if a drive that uses the usb cable as its sole power source is much slower than a drive with an external power source?

I'm only considering usb powered drives because I don't want to clutter my desktop with power cords (one of the main reasons I'm going with the all in one imac)

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migrated from Dec 14 '10 at 6:18

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This isn't really a SO question... but I suspect you'd be better off with a powered drive if you're intending not to use it. Firewire can provide much power (40V or so IIRC) so maybe you can fully power a drive with it. – Robert Dec 14 '10 at 3:57
You should probably consider an external RAID 1 drive over firewire. That way you get the speed and the safety. – Anders K. Dec 14 '10 at 4:15

Most 2.5" drives are USB-powered. Being USB-powered doesn't determine its speed as that is usually fixed (e.g. 5400 rpm or 7200 rpm with a given access time). In any case, the USB bus is the bottleneck in terms of data transfer. Having said that, no media that I have viewed has been limited during playback from the external drive. When transferring a bunch of media to/from the external, there is a noticeable slowdown versus transferring between two internal drives on a SATA bus.

However, all of this is moot if you would like a 1-2 TB drive. That capacity is currently only available for 3.5" drives, and I'm not aware of 3.5" external enclosures that are only USB-powered (or Firewire-powered, as one of the commenters above suggests).

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