For most of the history of commercial IT, servers have been measured largely by one metric: performance related to cost of acquisition. However, that equation, often known by the Americanism “bang per buck”, is now being challenged by a new metric called “performance per watt”.

The rise of performance per watt as a concern among IT buyers is a recognition that energy costs and, in particular, the power required by volume servers, have become important contributors to overall IT expense, even if the bill is still more likely to be handed to facilities managers than IT chiefs.

As Sun chairman Scott McNealy has written: “If the chief information officer isn’t calculating the cost of electricity in his purchasing decisions, the company may as well be burning money.”

The reasons for new interest in server power consumption relate not just to the rising cost of energy but also the sheer number of servers being installed in organisations. The rise of LANs in the 1980s, Windows servers in the 1990s, and more recently Linux servers, has seen low-cost servers proliferate, while the emergence of blade servers in the past few years has allowed companies to deploy many ultra-thin, low-cost servers that save on floor space and allow incremental additions to compute capacity. The flip-side of all this new hardware has been a leap in the power required by datacentres.

The changing nature of datacentres and soaring power costs have forced hardware makers to re-examine server design. Designers of microprocessors have been particularly active as experts state that the CPU is responsible for half or more of the total power consumed by low-end servers.

Many of the tricks designers are using in servers have their roots in mobile computer designs. Intel, for example, uses similar technology to its SpeedStep for notebook PCs to reduce server power consumption in its Demand Based Switching (DBS) technology. DBS allows clock speed and voltage to be throttled down when peak performance is not required, thereby saving electricity. AMD uses a similar capability called PowerNow in server chip designs.

The company that has perhaps done most to market energy awareness is Sun. Sun has managed to integrate eight cores on its latest Sparc chips. This compares with the two cores Intel and AMD can currently pack on one CPU. Also, on recent Sun chips, each core can execute four threads, further improving power efficiency without compromising performance.

Such is the significance of the transition from “bang per buck” to “performance per watt” that some, including Sun and AMD, see the need for an entirely new benchmarking system. Industry leaders are also backing The Green Grid, a group for IT professionals who aim to define best practices for server power management.

But many industry watchers believe that without further regulation the computer industry will only chip away at the power problem. Just as the US government’s Energy Star badge scheme helped reduce desktop power consumption, a similar mandate might be required for servers, they argue.