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Advanced Power Management Configuration for PC's and laptops

Updated on July 24, 2011

Most of the new laptops and PC's have Advanced Power Management (APM) or Advanced Configuration and Power Interface (ACPI) as standard. The whole point in these specifications is to manage how the system components use and conserve the power. Obviously this is very important for laptops when they are running on battery power.

Overview of ACPI standards

The ACPI standard describes how the power management features should be utilized in desktops and laptops. For a PC to be ACPI-compliant, it should have both the hardware and the software operating system supporting the ACPI standards. The ACPI standards define various states of the computer components.

Global states

The G0 state defines the normal working state of the PC. This state states that all devices and applications are running normally.

The G1 state defines the power-saving or sleep mode. G1 is then further divided into four other states: S1, S2, S3, and S4.


This is the most power-hungry sleep mode. Applications are stopped but only the unused devices are turned off. This can be happening naturally while you use your PC, if you are just doing a single task, and not using every component at the same time.


This is a deeper sleep state than the S1 state. With this the CPU is turned off and the computer uses much less power. You won't be using the PC at this point. This state could be activated during leaving your PC for an extended time.


This state is called standby mode in Windows. The power is maintained only to the RAM memory. Also called Suspended, since the RAM holds all information for applications you are currently working on. This allows you to start up your PC again quick, and resume where you were working.


This state is called hibernation mode in Windows and as Safe Sleep in the Mac OS. The information in the RAM is written to the hard disk, and the RAM is turned off completely. If you want to minimize your power, and maximize the time to get things going then this is the recommended state. It can take a few minutes though for your pc to copy the data back into the memory when it wakes up.

After the options of G1 States you also have:


This describes the soft power off mode, which means the computer is turned off by using the Shut Down button in your operating system.


This is complete off state, where you finally switch off using the power at the main switch.

Processor states

The Processor power states that are defined are C0 is the normal operation mode, C1 is the halt mode when means the processor can instantaneously come back to its duties, C2 is the stop-clock mode that uses much less power than the C1 mode, and then the C3 is the sleep mode when the CPU clears all its cache.


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