With reportedly more than 1 million servers scattered in three dozen data centers around the world, Google is spending billions of dollars to build large-scale facilities in Pryor, Okla.; Council Bluffs, Iowa; Lenoir, N.C.; and Goose Creek, S.C. Last year the company released its Google App Engine, a cloud-based platform that individuals and businesses can use to run applications. Microsoft, whose Quincy facility will house the initial version of its Windows Azure cloud-based operating system, is constructing additional facilities in Chicago, San Antonio, and Dublin, at roughly US $500 million each. The company is also said to be looking for a site in Siberia.

Designing bigger and better data centers requires innovation not only in power and cooling but also in computer architecture, networking, operating systems, and other areas. Some engineers are indeed quite excited by the prospect of designing computing systems of this magnitude—or as some Googlers call them, ”warehouse-size computers.”

The big data centers that went up during the dot-com boom in the late 1990s and early 2000s housed thousands, even tens of thousands, of servers. Back in those days, facility managers could expand their computing resources almost indefinitely. Servers, storage systems, and network equipment were—and still are—relatively cheap, courtesy of Moore’s Law. To get the computing power you needed, all you had to do was set up or upgrade your equipment and turn up the air-conditioning.

But in recent years, this approach has hit a wall. It became just too expensive to manage, power, and cool the huge number of servers that companies employ. Today’s largest data centers house many tens of thousands of servers, and some have reportedly passed the 100 000 mark. The data centers of the dot-com era consumed 1 or 2 MW. Now facilities that require 20 MW are common, and already some of them expect to use 10 times as much. Setting up so many servers—mounting them onto racks, attaching cables, loading software—is very time-consuming. Even worse, with electricity prices going up, it’s hugely expensive to power and cool so much equipment. Market research firm IDC estimates that within the next six years, the companies operating data centers will spend more money per year on energy than on equipment.

The data centers of the dot-com era consumed 1 or 2 megawatts. Now facilities that require 20 megawatts are common, and already some expect to use 10 times as much

What’s more, the environmental impact of data centers is now on the radar of regulators and environmentally conscious stakeholders. The management consulting firm McKinsey & Co. reports that the world’s 44 million servers consume 0.5 percent of all electricity and produce 0.2 percent of all carbon dioxide emissions, or 80 megatons a year, approaching the emissions of entire countries like Argentina or the Netherlands.

Data center designers know they must do many things to squeeze more efficiency out of every system in their facilities. But what? Again, companies don’t want to give the game away. But in their efforts to demonstrate the greening of their operations, Google, Microsoft, and others have revealed some interesting details. And of course, a number of innovations come from the vendor side, and these equipment suppliers are eager to discuss their offerings.

First, consider the server infrastructure within the data center. Traditionally, servers are grouped on racks. Each server is a single computer with one or more processors, memory, a disk, a network interface, a power supply, and a fan—all packaged in a metal enclosure the size of a pizza box. A typical dual-processor server demands 200 watts at peak performance, with the CPUs accounting for about 60 percent of that. Holding up to 40 pizza-box-size servers, a full rack consumes 8 kilowatts. Packed with blade servers—thin computers that sit vertically in a special chassis, like books on a shelf—a rack can use twice as much power.

The new large-scale data centers generally continue to use this rack configuration. Still, there’s room for improvement. For one, Microsoft has said it was able to add more servers to its data centers simply by better managing their power budgets. The idea is that if you have lots of servers that rarely reach their maximum power at the same time, you can size your power supply not for their combined peak power but rather for their average demand. Microsoft says this approach let it add 30 to 50 percent more servers in some of its data centers. The company notes, however, that this strategy requires close monitoring of the servers and the use of power-control schemes to avoid overloading the distribution system in extreme situations.

How the servers are set up at Google’s data centers is a mystery. But this much is known: The company relies on cheap computers with conventional multicore processors. To reduce the machines’ energy appetite, Google fitted them with high-efficiency power supplies and voltage regulators, variable-speed fans, and system boards stripped of all unnecessary components like graphics chips. Google has also experimented with a CPU power-management feature called dynamic voltage/frequency scaling. It reduces a processor’s voltage or frequency during certain periods (for example, when you don’t need the results of a computing task right away). The server executes its work more slowly, thus reducing power consumption. Google engineers have reported energy savings of around 20 percent on some of their tests.