Wired has an article on being more energy efficient in the data center using mobile DRAM. What few people know is RAM is a top energy consumer in servers after the processors. More than HD for many servers that are meant for memory intensive applications.
Over the past decade, the very concept of the server has evolved. Once, servers were giant machines jam-packed with processors and memory that focused on processing speed above all else. But nowadays, most servers are smaller and cheaper, and they consume less power. Services like Google Search and Microsoft Bing run on thousands of commodity machines, not the big beefy database servers hawked by companies like Oracle. When you’re serving millions of people across the globe, you can’t afford those power-hungry machines.
Here is the paper referenced in the wired article.