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ACM Queue - Power Management


Cooling the Data Center

Wed, 10 Mar 2010 17:52:56 GMT

Power generation accounts for about 40 to 45 percent of the primary energy supply in the US and the UK, and a good fraction is used to heat, cool, and ventilate buildings. A new and growing challenge in this sector concerns computer data centers and other equipment used to cool computer data systems. On the order of 6 billion kilowatt hours of power was used in data centers in 2006 in the US, representing about 1.5 percent of the country's electricity consumption. Of this power demand, much more than 20 percent is typically used for cooling the computer equipment, but some newer installations have managed to reduce consumption through a series of innovations in the design of data-center cooling systems, as well as improvements in the software and hardware.

Toward Energy-Efficient Computing

Wed, 17 Feb 2010 21:01:53 GMT

By now, most everyone is aware of the energy problem at its highest level: our primary sources of energy are running out, while the demand for energy in both commercial and domestic environments is increasing, and the side effects of energy use have important global environmental considerations. The emission of greenhouse gases such as CO2, now seen by most climatologists to be linked to global warming, is only one issue.

A Conversation with Steve Furber

Mon, 01 Feb 2010 11:45:50 GMT

If you were looking for lessons on energy-efficient computing, one person you would want to speak with would be Steve Furber, principal designer of the highly successful ARM (Acorn RISC Machine) processor. Currently running in billions of cellphones around the world, the ARM is a prime example of a chip that is simple, low power, and low cost. Furber led development of the ARM in the 1980s while at Acorn, the British PC company also known for the BBC Microcomputer, which Furber played a major role in developing.

Power-Efficient Software

Fri, 08 Jan 2010 19:25:50 GMT

The rate at which power-management features have evolved is nothing short of amazing. Today almost every size and class of computer system, from the smallest sensors and handheld devices to the "big iron" servers in data centers, offers a myriad of features for reducing, metering, and capping power consumption. Without these features, fan noise would dominate the office ambience, and untethered laptops would remain usable for only a few short hours (and then only if one could handle the heat), while data-center power and cooling costs and capacity would become unmanageable.

Maximizing Power Efficiency with Asymmetric Multicore Systems

Fri, 20 Nov 2009 12:34:20 GMT

In computing systems, a CPU is usually one of the largest consumers of energy. For this reason, reducing CPU power consumption has been a hot topic in the past few years in both the academic community and the industry. In the quest to create more power-efficient CPUs, several researchers have proposed an asymmetric multicore architecture that promises to save a significant amount of power while delivering similar performance to conventional symmetric multicore processors.

Powering Down

Thu, 17 Jan 2008 10:49:21 GMT

Powering Down

Smart power management is all about doing more with the resources we have.


Power management—from laptops to rooms full of servers—is a topic of interest to everyone. In the beginning there was the desktop computer. It ran at a fixed speed and consumed less power than the monitor it was plugged into. Where computers were portable, their sheer size and weight meant that you were more likely to be limited by physical strength than battery life. It was not a great time for power management.

Now consider the present. Laptops have increased in speed by more than 5,000 times. Battery capacity, sadly, has not. With hardware becoming increasingly mobile, however, users are demanding that battery life start matching the way they work. People want to work from cafes. Long-haul flights are now perceived as the ideal opportunity to finish a presentation. Two hours of battery life just isn’t going to cut it; users are looking for upwards of eight hours. What’s drawing that power, and more importantly, how can we manage it better?

Modern System Power Management

Fri, 05 Dec 2003 11:23:46 GMT

Modern System Power Management

Increasing demands for more power and increased efficiency are pressuring software and hardware developers to ask questions and look for answers.

The Advanced Configuration and Power Interface (ACPI) is the most widely used power and configuration interface for laptops, desktops, and server systems. It is also very complex, and its current specification weighs in at more than 500 pages. Needless to say, operating systems that choose to support ACPI require significant additional software support, up to and including fundamental OS (operating system) architecture changes. The effort that ACPI’s definition and implementation has entailed is worth the trouble because of how much flexibility it gives to the OS (and ultimately the user) to control power management policy and implementation.


Of course, power management wasn’t initially part of the PC platform at all. Early mobile computers were mobile only in the loosest sense. Some didn’t even have batteries. If they did, they could be operated only briefly away from an AC outlet. From a software perspective, DOS, the PC’s first operating system, was generally unaware that it was running on a mobile PC at all. Very early on, manufacturers added value to their systems by implementing support for “suspend-to-RAM” functionality and LCD screen blanking. Early CPUs with mobile features, starting with the Intel 80386SL, added a special system management mode (SMM), in which the firmware (also referred to as the BIOS) could more easily perform power management and other functions without requiring OS support.

Making a Case for Efficient Supercomputing

Fri, 05 Dec 2003 11:21:00 GMT

Making a case for Efficient Supercomputing

It’s time for the computing community to use alternative metrics for evaluating performance.

A supercomputer evokes images of “big iron” and speed; it is the Formula 1 racecar of computing. As we venture forth into the new millennium, however, I argue that efficiency, reliability, and availability will become the dominant issues by the end of this decade, not only for supercomputing, but also for computing in general.

Over the past few decades, the supercomputing industry has focused on and continues to focus on performance in terms of speed and horsepower, as evidenced by the annual Gordon Bell Awards for performance at Supercomputing (SC). Such a view is akin to deciding to purchase an automobile based primarily on its top speed and horsepower. Although this narrow view is useful in the context of achieving “performance at any cost,” it is not necessarily the view that one should use to purchase a vehicle. The frugal consumer might consider fuel efficiency, reliability, and acquisition cost. Translation: Buy a Honda Civic, not a Formula 1 racecar. The outdoor adventurer would likely consider off-road prowess (or off-road efficiency). Translation: Buy a Ford Explorer sport-utility vehicle, not a Formula 1 racecar. Correspondingly, I believe that the supercomputing (or more generally, computing) community ought to have alternative metrics to evaluate supercomputers—specifically metrics that relate to efficiency, reliability, and availability, such as the total cost of ownership (TCO), performance/power ratio, performance/space ratio, failure rate, and uptime.

Energy Management on Handheld Devices

Fri, 05 Dec 2003 11:18:26 GMT

Energy Management on Handheld Devices

Whatever their origin, all handheld devices share the same Achilles’ heel: the battery.

Handheld devices are becoming ubiquitous and as their capabilities increase, they are starting to displace laptop computers—much as laptop computers have displaced desktop computers in many roles. Handheld devices are evolving from today’s PDAs, organizers, cellular phones, and game machines into a variety of new forms. Although partially offset by improvements in low-power electronics, this increased functionality carries a corresponding increase in energy consumption. Second, as a consequence of displacing other pieces of equipment, handheld devices are seeing more use between battery charges. Finally, battery technology is not improving at the same pace as the energy requirements of handheld electronics. Therefore, energy management, once in the realm of desired features, has become an important design requirement and one of the greatest challenges in portable computing, and it will remain so for a long time to come.

Among today’s rechargeable batteries, lithium-ion cells offer the highest capacity. Introduced commercially by Sony in 1991, their capacity has improved by about 10 percent per year in recent years [1]. This rate of improvement is leveling off, however, and even with alternative materials and novel cell structures, major future improvement in rechargeable batteries is unlikely.

The Inevitability of Reconfigurable Systems

Fri, 05 Dec 2003 11:15:13 GMT

The Inevitability of Reconfigurable Systems

The transition from instruction-based to reconfigurable circuits won’t be easy, but has its time come?

The introduction of the microprocessor in 1971 marked the beginning of a 30-year stall in design methods for electronic systems. The industry is coming out of the stall by shifting from programmed to reconfigurable systems. In programmed systems, a linear sequence of configuration bits, organized into blocks called instructions, configures fixed hardware to mimic custom hardware. In reconfigurable systems, the physical connections among logic elements change with time to mimic custom hardware. The transition to reconfigurable systems will be wrenching, but this is inevitable as the design emphasis shifts from cost performance to cost performance per watt. Here’s the story.


Until the 1940s, solving problems meant building hardware. The engineer selected the algorithm and the hardware components, and embedded the algorithm in the hardware to suit one application: fixed hardware resources and fixed algorithms. The range of applications amenable to hardware solutions depended on the cost and performance of hardware components.