DURHAM, N.C. -- Duke University computer scientists are developing a new approach to managing electric power use by computers. Their Milly Watt" project not only promises to greatly increase the energy efficiency of computers, but alleviate the frustration of computer users who find their laptops or desktops abruptly shutting down because of drained batteries or unwanted "decisions" by the machines' power management software.

What's more, the project promises greater energy efficiency in computers that are an increasing drain on the electric power system, said the scientists -- Carla Ellis, Alvin Lebeck, Amin Vahdat and their associates.

The basic concept of the Milly Watt project, say the scientists, is that computers would use energy more wisely if the machines treated it like money. Their Energy-Centric Operating System (ECOSystem) uses energy units called "currentcy" to put computing tasks and devices on a budget. ("Currentcy" is a coined term combining "currency" and "current".)

The researchers are presenting a paper June 12 at USENIX, an annual technical conference of the Advanced Computing Systems Association., in which they describe new refinements in ECOSystem, including provisions for tracking the energy needs of competing software programs and smoothing out the variations in response time that happen when available energy is limited.

Another "Face-Off" system under development by the Duke computer scientists features a camera that determines whether there is, indeed, a human user sitting in front of the computer.

"Under the ECOsystem, when tasks have used up their currentcy, they have to stop spending," Ellis said. "When the total currentcy available is small, spending has to be lower across the board. This approach beats waiting until you notice a component hasn't been doing any real work for 10 minutes and then shutting it down."

ECOSystem is the centerpiece of the larger Milly Watt energy-management research program, which even features a trademark cartoon character meant to resemble the popular General Electric symbol, Reddy Kilowatt. However, while Reddy was the electricity industry's supersalesman for everything that consumed more electricity, Milly Watt stands ready to reduce energy consumption and extend battery life for the mobile millions who take electronics everywhere.

The stage is set for Milly Watt to become a star, said Ellis. Notebook computers, handhelds and hybrid wireless phone-computers have brought computer users unprecedented freedom of movement, but at the price of constant vigilance on battery life. "Small size makes mobile computers mobile, but batteries make them run, and batteries never last long enough," said Ellis

Mobile computing is only one of the forces driving the need for improved power management in electronic devices, she said. Power management in all kinds of computers can also reduce environmental effects and energy expenses, said Ellis

Power management has progressed since the days of leaving all the computer components constantly on. Individual computer components have been engineered to draw less power, and operating systems can shut down idle components such as disk drives and ratchet down the voltage available to processors. However, progress in managing power has been offset by increased demands for raw power as computer operating speeds increase, Ellis noted. The original IBM PC needed a maximum of 63 watts of power. Many of today's models need 300 or even 400 watts. Also, the faster processors in today's notebook computers burn power fast, Ellis said.

Previous approaches to power management have tried to manage energy one component at a time. The primary goal has been to spot idleness and eliminate waste since the battery will last longer if less energy is wasted. However, these approaches offer little control over how the available power is divided up.

In ECOSystem, "Currentcy provides a mechanism for energy accounting and allocation," said Ellis. "ECOSystem won't schedule a process for execution if it can't pay up."

Like real money, a unit of currentcy has a very specific definition. It is one one-hundredth of a millijoule. (Lighting a one-watt lamp for one second takes one joule of power.) In one ECOSystem test, using a hard disk for 90 seconds took about 6,000 milliJoules, or 600,000 units of currentcy.

Lebeck noted that Milly Watt takes the unusual step of managing power allocated to system memory. "Memory has been the unturned stone in low-power research and yet it can consume a significant proportion of the power in small mobile devices. We offer techniques for exploiting memory chips that can power down without losing data."

The currentcy mechanism makes it possible for the user to specify a desired battery lifetime and manage power to make the charge last that long. ECOsystem calculates an acceptable discharge rate from the current time and the target lifetime. The system controls the rate of discharge by first dividing time into intervals. At the beginning of each interval, with the remaining battery charge known, the system makes a decision about the total currentcy that can be used during the interval. Then, the currentcy is divided up among tasks so that the more important ones get a bigger allowance. As tasks use various parts of the hardware (e.g., central processing unit, disks, network interface card, memory), currentcy is debited from the task's account to pay it. The process of allocating currentcy and debiting each task's account repeats for each interval until the battery lifetime is lived out.

"The idea is to live within a balanced budget for your whole lifetime rather than waiting for the bank account to run low and then panicking," Lebeck said. "Tasks can also cooperate to get better deals -- lower prices for accessing devices more efficiently."

The "FaceOff" project seeks to reduce power consumption by using a video camera and face-detection software to sense the user's presence and intention. The display is usually the second biggest power hog to the processor, said Ellis.

"The display is only there for the user to look at," she said. "If the user leaves or is just listening to music, the display is drawing power unnecessarily. On the other hand, who hasn't been reading the display and had it go blank because the keyboard and mouse haven't been touched for a few minutes? We think face recognition can help improve judgments about when the display can be powered down."

Added Ellis, "The display, like every other component and activity in a computer system, depends on energy. That's why Milly Watt makes conserving energy a central mission of the operating system. Reddy Kilowatt had his day. Milly Watt is what the world needs now."