Calxeda’s system on chip for servers uses energy-efficient ARM processors normally used in smart phones and tablets. Credit: Calxeda

Calxeda recognized that the cell phone industry had something to teach server vendors: how to save power.

The Austin, Texas-based startup yesterday said it has raised $55 million in venture funding round led by Vulcan Capital and Austin Ventures. It’s raised over $100 million to date and will use the new money to further invest in its ultra low-power server design.

Calxeda took on the problem of heavy energy use in data centers by turning to the ARM processor, a chip used in smart phones and tablets which are optimized for power efficiency. The company has made a system-on-a-chip that includes multi-core ARM processors and a dedicated chip for coordinating data networking between processors.

With its technology, a server can use as little as five watts and reduce its idle power to less than one watt. Tests show that its systems improve energy efficiency ten-fold over servers built with X86 processors from Intel or AMD, the company says.

Calxeda puts four of its EnergyCard systems-on-a-chip onto a single board. HP has built a server that packs 288 of these server boards into a 4U chassis. That means data center operators can put a lot of computing power in a relatively small space without causing heat problems from power. Those HP servers are expected to be available later this year.

The investor interest in Calxeda reflects big changes in data centers. Rather than general-purpose servers, technology companies are developing hardware to fit a type of computing load.

Servers built with Calxeda’s chips are well suited for “scale out” architectures where many low-cost servers are strung together to, for example, serve up Web pages or content to mobile devices. Dell earlier this year showed off a server built around ARM processors designed for these types of jobs.

Data center operators are also seeking out ways to save power to lower their costs and environmental footprint, which has spurred innovation in semiconductors. Competitor SeaMicro, which was acquired by AMD, is another company that developed new Intel-based servers optimized for efficiency.

HP has built a server using as many as 288 server boards in the space of a 4U server chassis. Credit: Calxeda.