Bus-powered hard drives and older Mac laptops

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In our recent review of Western Digital’s My Passport Studio ( ) portable hard drive, we spent quite a bit of time discussing the drive’s cables and power requirements. In our tests, conducted with both a Mac Pro and a MacBook Pro, we found that the drive—which doesn’t come with a power supply—can successfully use the power from both the USB and FireWire ports on our test systems.

After we posted our review, it didn’t take long for a reader to comment that the drive does not work with a PowerBook. Western Digital’s documentation does acknowledge that some computers do not supply enough power over USB for the drive to operate. In those cases, you need an optional $10 USB 2.0 Power Booster Cable that connects to a pair of USB ports on the computer. Western Digital doesn’t list specific computer models that might require this optional cable. According to a Western Digital representative, anyone who buys the drive and needs the Power Booster cable can get one for free by contacting Western Digital’s customer support at 800-275-4932.

Don’t be quick to blame Western Digital, however. PowerBook users would run into the same problem with nearly any other bus-powered portable USB hard drive. We thought it would be valuable to offer a more specific list of Macs that provide enough USB juice to power a drive like the My Passport Studio, as well as those that don’t.

To that end, I tested a plethora of Macs, and I can confirm that when using a standard USB A to mini-USB B cable, the drive will operate perfectly fine on a MacBook, MacBook Pro, MacBook Air, iMac G4, iMac G5, Intel iMac, Mac Pro, PowerMac G4, and PowerMac G5.

However, if you happen to have an earlier-model portable Mac, like a PowerBook or an iBook, the USB ports on these Macs supply enough power to turn the drive on, but they cannot support the current that spinning up a hard drive requires (we found this to be the case with the iBook G3, iBook G4, a 15-inch PowerBook G4, and a 17-inch PowerBook G4). Interestingly, the PowerBook G3 400 (FireWire/Pismo) was the only pre-Intel laptop to successfully power the Western Digital drive over USB. Some companies, like Wiebetech and Other World Computing, use an external power supply to make up for bus power shortcomings, rather than the dual USB approach that Western Digital uses.

Western Digital’s 22-inch USB 2.0 Power Booster Cable seems designed for 17-inch (and larger on the PC side) laptops. The cable’s mini-USB B connector fits into the My Passport Studio, and the two USB A connectors fit into a laptop’s two USB ports. However, the cable is rather ungainly when using it with an iBook, where the USB ports are right next to one another—the length of the Power Booster Cable then seems like a bit much. The cable does work, but at the expense of occupying both of your USB ports, which rules out the use of external keyboards, digital cameras, printers, iPods, and anything else that uses a USB connection. Unless you use a powered USB hub.

The only mobile Mac that lacks a FireWire connection is the MacBook Air. Our tests showed that the My Passport Studio works fine with the MacBook Air using the bundled USB cable and a single USB port.

When given the option between a USB and FireWire connection, of course you should opt for FireWire’s faster speed. There will be times when you absolutely have to use USB, like when using a FireWire device such as a camcorder, or if you’re without a FireWire cable. You can also boot from an external drive over FireWire in the event of an emergency (PowerPC Macs included).

[Blair Hanley Frank is an intern at Macworld.]

[Editor's note: Updated on 7/10 at 1:40 p.m. Pacific to add information about the Power Booster cable.]

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