There are a lot of "green" hard drives out there, which claim to be low-power, low-noise, low-heat, and low-cost. Sadly, they don't save quite as much power as they claim, and here's why.
There isn't anything wrong with buying a low-powered drive—after all, we used one in our second Hackintosh build. While drives like the Western Digital Caviar Green are a bit cheaper than their faster counterparts (since they only run at 5400RPM), the "power saving" promise falls short, as they only save you a few watts. Ars Technica explains:
In terms of cost, using a green hard drive compared to a normal one makes very little difference. 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.
If you're installing a drive into an HTPC, they're probably a good choice since they are a bit quieter and cooler than other drives, and you don't need the drive performance anyways. But if you're building something you'll actually be computing on, you won't be saving any power or money with the green drive—you'll just be slowing your machine down (albeit at a somewhat lower upfront cost). Hit the link to read more.
Skip the "Green" Hard Drives If You're Trying to Save Power