It's what's inside those trailers, though, that’s key to Microsoft's cloud-computing efforts. Each of shipping containers in Chicago data center houses anywhere from 1,800 to 2,500 servers, each of which can be serving up e-mail, managing instant messages, or running applications for Microsoft's soon-to-be-launched cloud-based operating system--Windows Azure. Upstairs, Microsoft has four traditional raised floor server rooms, each roughly 12,000 square feet and consuming, on average, 3 megawatts of power. It's all part of a data center that’ll eventually occupy 700,000 square feet, making it one of world's largest: