Conclusions
Kermit was right: it ain't easy being green, er, power. Dialing back the Caviar GP's spindle speed predictably slows the drive, making the GreenPower a poor choice if you're looking for fast sequential transfer rates, quick load times, or great performance with disk-intensive multitasking loads.

Fortunately, there's more to the performance picture for the Caviar GP. Western Digital was only aiming for "solid" performance with the drive, and they've largely achieved it. The GreenPower performed well in WorldBench, for example, so it's a perfectly acceptable drive for mainstream desktop applications. Performance in IOMeter was surprisingly good, too, making it tempting to recommend the GP for power-efficient enterprise storage. Sure, it's not optimized for RAID environments like Western Digital's enterprise-class products, but the power savings will add up in multi-drive environments.

Lower power consumption was Western Digital's primary goal with the GreenPower, and they've nailed it. The Caviar GP is the most power-efficient drive we've ever tested, and that's saying a lot considering its terabyte capacity. No other high-capacity drive even comes close, and Hitachi's terabyte Deskstar sucks twice the power of the GP under load.

We expected the GreenPower to be energy-efficient. What we didn't expect was the drive's incredibly low noise levels. The GreenPower makes less noise than any other 3.5" drive we've tested, particularly at idle, where it's barely audible. That makes this drive perfect for home theater PCs, where its terabyte capacity is ripe for HD recording, and also for silent desktops where noise levels take precedence over performance.

The icing on the cake for the Caviar GP is the fact that the drive is actually quite affordable. With street prices as low as $288 online, the GreenPower is 10% cheaper than its nearest terabyte rival. That sounds just about right given the drive's performance, making it easy to recommend the Caviar GP to anyone looking to lower his PC's noise levels or power consumption.