Cool'n'Quiet

AMD Cool'n'Quiet is a CPU dynamic frequency scaling and power saving technology introduced by AMD with its Athlon XP processor line. It works by reducing the processor's clock rate and voltage when the processor is idle. The aim of this technology is to reduce overall power consumption and lower heat generation, allowing for slower cooling fan operation. The objectives of cooler and quieter result in the name Cool'n'Quiet. The technology is similar to Intel's SpeedStep and AMD's own PowerNow!, which were developed with the aim of increasing laptop battery life by reducing power consumption.
Due to their different usage, Cool'n'Quiet refers to desktop and server chips, while PowerNow! is used for mobile chips; the technologies are similar but not identical. This technology was also introduced on "e-stepping" Opterons, however it is called Optimized Power Management, which is essentially a re-tooled Cool'n'Quiet scheme designed to work with registered memory.
Cool'n'Quiet is fully supported in the Linux kernel from version 2.6.18 onward and FreeBSD from 6.0-CURRENT onward.

Implementation

In-order to take advantage of Cool'n'Quiet Technology in Microsoft's Operating Systems:Cool'n'Quiet should be Enabled in system BIOS

In Windows XP and 2000: Operating Systems "Minimal Power Management" profile must be active in "Power Schemes". A PPM driver was also released by AMD that facilitates this.
In Windows Vista and 7: "Minimum processor state" found in "Processor Power Management" of "Advanced Power Settings" should be lower than "100%".

Also In Windows Vista and 7 the "Power Saver" power profile allows much lower power state than in the "High Performance" power state.
Unlike Windows XP, Windows Vista only supports Cool'n'Quiet on motherboards that support ACPI 2.0 or later.
With earlier versions of Windows, processor drivers along with Cool'n'Quiet software also need to be installed. The latest version is 1.3.2.0.

Processors supporting Cool'n'Quiet

Athlon XP
Athlon 64 and X2 – all models
Athlon 64 FX – FX-53 and higher
FX
Athlon II – all models
Sempron – Socket 754: 3000+ and higher; Socket AM2: 3200+ and higher
Opteron – E-stepping and higher, branded as Optimized Power Management
Phenom – all versions support Cool'n'Quiet 2.0
Phenom II – supports Cool'n'Quiet 3.0
some of the APUs
Ryzen – 3, 5, 7, and 9 all models support Cool ‘n’ Quiet
EPYC