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Introduction

Due to some confusion I see on the net, when it comes to AMD and Intel power saving functions, I have tried to make a simple guide and explanation to the various settings you can make on the chipsets.

This should hopefully help when you to better understand what these settings do if you’re unsure of what they actually do.
I haven’t added all the C-state power modes yet, but may eventually get to it.

Please note Intel and AMD may use exactly the same name for certain C-states, like C1E, but it doesn’t mean they are exactly the same! (Confusing I know >.<).

I'm sure a lot of people already know this in here, but I haven't been able to find a guide in here for it yet.

Intel

EIST: A dynamic state, which via software allows the processor to only use the performance needed for the program. This in turn minimizes heat and power draw, as it automatically reduces the power if the program you’re running requires less processing power.

Problems reported by Microsoft has been previewing certain video files, and may make overclocking unstable.

C1E: Puts your processor into a power-saving mode if your processor is idle. Reduces your CPU-clock and voltage by stopping the CPU internal clock.
The difference between normal C1 and C1E (Enhanced mode) is that C1 doesn’t reduce voltage, but only reduce the CPU internal clock. All newer Intel chipsets have C1E.


AMD

Cool’n’Quiet: The equivalent of Intel’s EIST.

C1E: To make things confusing AMD also uses the C1E name like Intel, but it is a completely different thing.
When the processor enters the state it cuts all internal clock signals from the CPU, including the clocks from the bus interface unit. This means when the CPU enters this sleep mode it can’t answer to important requests coming from the CPU external bus nor interruptions.

This is exactly like the C3 state, but the main difference is that the AMD C1E enters this sleep state automatically, where with C3 you usually need a command by your operating system.