Every year, computing devices--from cell phones to servers--consume at least 125 terawatt-hours of electricity, roughly the amount produced by burning 350 million tons of coal. Partha Ranganathan, principal research scientist at Hewlett-Packard Labs, is developing strategies to bring that figure down (see below). "All the ideas are very intuitive," he says. "But we needed to solve some hard problems to get there." Technologies he helped develop, which could save money and lower greenhouse-gas emissions, are already starting to appear in consumer and business products.

Taking a bite out of the energy pie:
Estimated savings, as a percentage of power used globally by computing devices (assuming widespread adoption of these strategies). Scroll over the pie chart for a description of each part.

--David Talbot