The cost benefits come partly from economies of scale. Shipping 2,000 servers in a container is more cost-effective than shipping and installing separate racks, and portable datacenters don't require raised floors or as much wiring.

They can offer a better "power unit efficiency" ratio than do traditional datacenters, he said. PUE is a measure of a datacenter's power efficiency. If a server demands 500 watts and the PUE of a datacenter is 3.0, the power from the grid needed to run the server will be 1,500 watts, according to a definition from the Green Grid industry consortium.

"We've seen PUE at a peak of 1.3" in modular datacenters, Costello said, compared with between 1.6 and 2.0 for a traditional datacenter.

The containers can accommodate 1,000 watts per square foot, allowing companies to power a lot more servers in a given area, he said. Many companies are unable to add more equipment to their datacenters because power supplies and cooling equipment are at maximum capacity. The portable datacenters are an alternative to building new facilities or extending old ones.

There are some drawbacks and plenty of questions to be answered, he said. Some of the cons include a higher cost of failure if the power to a container is cut off, as well as new risks in terms of regulatory compliance. In addition, portable datacenters offered today can't accommodate servers from multiple vendors, he said.

There may also be issues with patents. The idea of putting standard equipment into a standard shipping container probably can't be patented, according to Costello, but "what happens inside the unit, in terms of airflow and how it's laid out, is definitely patentable."

There are also questions about the lifecycle of a portable datacenter, such as whether it can be refurbished after its 10-year lifespan or will need to be discarded. "The financial models are still being worked out," Costello said.

But he thinks portable datacenters will be deployed widely to provide services to end-users. "We used to talk about a PC on every desk," he said. "But how about a datacenter in every town?"

The company is looking at green energy sources to power them, including wind, solar, and hydroelectric, he said.

The Structure conference is about the infrastructure equipment needed for "cloud computing," which refers to hosted services such as Amazon's S3 storage service and Google's App Engine, but can also include online services such as MySpace and Salesforce.com.