“a 1TB Western Digital Caviar Green model that runs at 3.0 Gb/s with a 32MB cache consumes an average of 4.8 watts when reading or writing, 2.82 watts when idle, and 0.38 watts when in standby or sleep mode. A WD Caviar Black with the same specs consumes 8.4 watts when reading or writing, 7.8 when idle, and 1 in standby or sleep.”

“Assuming your drive spends 4 hours reading and writing and 20 hours idle per day, switching from the WD Black to Green saves you only 45 kilowatt-hours per year. The national average cost of a kilowatt-hour is 11.93 cents, netting you a whopping $5.38 per year for your sacrifice of 1800 RPM. For comparison, changing one 60-watt lightbulb used 4 hours a day to a 7-watt fluorescent one saves you more, about $9.23 per year.”

7200 RPM hard drives have been the mainstay in the desktop field for years now. Speeds remain constant while the price per gigabyte slowly falls off--today’s high capacity drives easily reach 2TB territory without costing an arm and a leg. Despite the popularity of these mass storage units, drivemakers have added a new category of HDDs to their offerings: slower “green” 5400 RPM units that promise lower power consumption and quieter, cooler operation. compare 7200RPM drives and 5400RPM drives to find out exactly how energy efficient “green” storage really is. Are they worth the money? Short answer: no. Here’s why.Ars found that a green Samsung drive used only about 2 fewer watts of power over its standard counterpart. And the trade off for minor power saving is, of course, speed--even though Western Digital’s 5400RPM drives are supposed to use the “IntelliPower” system to run somewhere between 5400 and 7200RPM, they’re definitely slower than the Caviar Black line.But here’s why green drives really don’t make a lot of sense when performance is still important:If you’re going completely green with all of your technology, or want a quiet HTPC or Network-attached storage unit as Ars suggests, green drives have their place. But if you really care about saving money on power consumption--and don’t want to sacrifice speed--get a solid-state drive. They’re faster, quieter, and draw less power.And you might want to give serious thought to changing out all those old incandescent light bulbs already. That reallysave you some money.