Cool'n'Quiet

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Cool'n'Quiet is a CPU speed throttling and power saving technology introduced by AMD with their Athlon 64 processor series. When the user is running undemanding applications and the load on the processor is light, the processor's clock speed and voltage are reduced. This in turn reduces its average power consumption.

This technology was introduced on new E-step Opterons branded as Optimized Power Management (OPM), basically a modified Cool'n'Quiet to work with registered RAM, in 2005.

Enabling Cool'n'Quiet

In Microsoft Windows;

Download the appropriate CPU driver from AMD[link]
Go to the Power Options in control panel and set the "Power scheme" to "Minimal Power Management". Setting it to "Portable/Laptop" will also work.
Ensure that the feature is set to "Enabled" or "Auto" in the BIOS.

To check that C'n'Q has successfully been installed, use a utility such as CPU-Z. When idle the system should work at 1GHz (if not overclocked), and a reduced voltage. Applications such as Crystal CPUID can use the C'n'Q drivers to perform a software based version, which allows the user to choose the CPU clock speed and voltage for a certain amount of CPU load. Some users have noted that doing so can result in "green dots" or "green squares" appearing in MPEG-4 video playback. In Linux, Cool'n'Quiet is supported by the powernow-k8 kernel module. In FreeBSD, it is supported by the cpufreq(4) kernel module. Full-time users of distributed computing applications such as Folding@Home will not notice any effect by enabling C'n'Q as their CPUs are constantly at full load.

Processors supporting Cool'n'Quiet

Athlon 64 - all models
Athlon 64 X2 - all models
Athlon 64 FX - FX-53 (Socket 939 only) and higher
Sempron - 3000+ and higher (except Socket A)
Opteron - E-step and higher, branded as Optimized Power Management
Mobile Athlon 64 - branded as PowerNow!
Mobile Sempron - branded as PowerNow!
Turion 64 - branded as PowerNow!

**List of CPU power saving technologies**
CPU power saving technologies Intel SpeedStep \| AMD Cool'n'Quiet \| AMD PowerNow! \| Transmeta LongRun \| Transmeta LongRun2 \| VIA LongHaul (italics indicate technologies for non-x86 processors)

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