Though the building alone covers a whopping 11 acres, you can't even see Microsoft 's new $550 million data center in the hills west of San Antonio until you're practically on top of it. But by that point, you can hardly see anything else.

These days, the massive data center is a bustling construction zone where visitors have to wear hardhats, helmets, orange safety vests, goggles and gloves. By September, it'll be the newest star in Microsoft's rapidly expanding collection of massive data centers, powering Microsoft's forays into cloud computing like Live Mesh and Exchange Online, among plenty of other as-yet-unannounced services. Pulling in, visitors are stopped by Securitas guards who check IDs and ask if they work for Microsoft. An incomplete gate marks the way. Microsoft's general manager of data center services, Mike Manos, won't say exactly what security measures will be in place when the data center opens, but won't rule anything out. "Will the gates be able to stop a speeding Mack truck?" I ask. "Or more," he responds. "Will you have biometrics?" "We have just about everything."