7. 'Solid-state drives use less energy than regular hard drives.'
At full brightness, with Wi-Fi and Bluetooth on and a regular hard drive installed, our MacBook Pro drew about 14W when idle. At the same settings, but with an SSD in place of the regular hard drive, the MacBook Pro drew just shy of 15W. When copying a 10GB file from the machine's desktop to a different folder on the same drive, the MacBook Pro drew 18.8W with the regular hard drive in place versus 20.1W with the SSD. When idle with Wi-Fi and Bluetooth on, the iMac averaged 82.7W using the hard drive and 77.6W with the SSD. In copying the file, however, the power savings disappeared, with the hard drive drawing approximately 85.3W while the SSD drew about 85.9W.
Takeaway: In our tests, the SSD appears to have used less power than the 3.5-inch, 7200-rpm hard drive in the iMac, but a bit more power than the 2.5-inch, 5400-rpm hard drive found in the stock MacBook Pro.
8. 'Bus-powered FireWire drives use more power than USB hard drives.'
We connected a Western Digital My Passport Studio drive equipped with both USB 2.0 and FireWire 800 ports to our 15-inch 2010 MacBook Pro. With the drive mounted (but idle) via USB 2.0, the MacBook Pro's display set to full brightness, and the laptop fully charged and with Bluetooth and Wi-Fi turned off, the Watts Up Pro meter reported a draw of about 16.1W. With the drive attached via FireWire (but idle), and all other conditions the same, the meter registered 18.4W. While we performed a Time Machine backup, the MacBook Pro with USB hard drive used 25.1W versus 28.2W over FireWire 800.
Takeaway: Our drive drew less power, whether idle or in use, when connected over USB than when connected via FireWire.
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