Intel manages to outclass its competitor AMD on yet another selling-point: idle power consumption has dropped to under 5W for its new 45nm-generation dualcore and quadcore chips.

Idle power consumption
While AMD is having a hang-over from a party gone awry, Intel is catching up in some areas AMD traditionally has a better record. One of those areas is idle power consumption, when the system is not using any significant amount of processor power. Since processors have become so fast, most of the time their processing power isn't required nor useful so becomes unused. Modern chips have advanced power-saving techniques, which can significantly lower the power consumption under these circumstances.

And the good thing is: most of the time, a computer is idling! Whether you are leaving your computer on between lunch or work on it, your system is being so lowly utilized that power saving will kick in. Emailing, chatting, listening to music, writting in office applications are all examples of common tasks which require relatively few processing power, allowing the processor to save a lot of power.

Power hogs
The real power hogs are 3D-games, since their inefficient endless-loop design will always consume 100% CPU (singlecore) even though the framerates are well beyond optimal levels (>75fps). Watching a 1080p High Definition movie with very high resolution and compression might also require too much processing power to let your CPU continue to run in power saving mode.

So idle power usage is more important than maximum power usage?
Yes! So do not rely on TDP for your "power consumption" but look at idle consumption instead. Besides, the maximum consumption is often well below the TDP value, as you can read here. For multicore chips it might be interesting to see the power savings when only one core is fully utilized.

How does the power saving work?
When the CPU is idling, power savers like AMD's Cool'N'Quiet and Intel's EIST will lower power consumption by reducing the voltage and frequency of the processor. The result is a drastic decrease in current leakage, resulting in lower power consumption. Hurray!

But what if I start an application and need processing power again? Well once the CPU is beyond a threshold utilization (say 65%) it will "ramp up" to a higher voltage and/or frequency, meaning the CPU will be faster but consumes more energy. It will continue to throttle until it reaches its maximum rated frequency and voltage, when required. The throttling goes so fast that performance decreases caused by the power saving techniques is minimal. So it shouldn't do any harm.

Future technology to save power
AMD's upcoming Turion Ultra chip has seperate power planes, allowing both cores to work at a different voltage and frequency. In the future, that would mean a chip with 64 or 128 cores will only need a few active when idling, causing hefty power savings. Plus, it combines both performance with power-efficiency.

How to enable power saving on my PC?
If you're using Windows, set your power scheme to "Minimal power saving", which you'll find in Control Panel -> Power options. Also, install the CPU driver for your processor, i.e. AMD. If you're on FreeBSD, make sure the cpufreq driver is loaded in kernel or via module and enable the power daemon powerd.

Why should i care about low-power?
you pay less on your electricity bill, resulting in savings that can be up to €150 a year for a single system.
your system runs cooler, because all consumed energy is converted into heat. Cool systems are more stable and potentially have a longer lifespan.
your systems runs quieter, since less cooling in terms of air movement is required to dissipate the generated heat. Some systems even allow operation without any active cooling, so no fans and zero noise!
you save money because valuable materials used by cooling such as copper and aluminium, will not be needed in large quantities. Modest heatsinks will be sufficient.
low-power components often have a lower failure rate; a CPU drawing 140W may cause material degradation, thereby shortening its lifespan.
you help save the environment by consuming less energy, thus producing less greenhouse gasses. Are you Co²-neutral yet?

Reducing power consumption is not only in the best interest of our environment, but also common business sense. The biggest challenge in modern cpu design is reducing power consumption; for it limits the scaling of frequency and thereby performance. A simple die-shrink (producing on new 45nm process instead of 65nm) should enable either higher performance by higher clock frequency or lower power drain if it keeps the same frequency. Power is everything(tm).

Intel versus AMD in idle power consumption
Up until now, Intel hasn't had much success in lowering the idle power consumption. The Pentium 4 turned into a power hungry underperformer (remember Prescott?) and the Core2Duo Conroe still consumed a hefty 25W when doing absolutely nothing!

AMD did much better, thanks primarily to the Cool'N'Quiet technology which lowers voltage and frequency on-the-fly. Most Athlon 64 processors do under 10W while being idle. Some single-core models even go as low as 1W, while the dualcore BE-series do about 4-5W. Phenom, the new but plagued quadcore chip from AMD, also will have a low-power version dubbed the 9100e (B2) and 9150e (B3, TLB bug corrected) which will launch in summer this year. It is still unclear how much energy this chip uses when idling.