Save as Your PC Sleeps
Modern PCs incorporate a power-management standard called the Advanced Configuration and Power Interface (ACPI), which allows the operating system, BIOS, and hardware to cooperate in reducing power consumption. ACPI defines several global power and sleeping states; our chart below lists the relevant ACPI states and corresponding Windows XP/Vista modes, along with the power used by each mode on the example system.
You've probably put your laptop into hibernation or sleep hundreds of times, but people typically ignore these features on desktops. As the chart shows, power use in the S3 state (Standby in XP, and Sleep in Vista) is nearly equal to that used when the PC is powered off. The S3 state drops PC power down to 10 watts or less when idle even if the system consumes considerably more power than average while active. Unfortunately, most PCs I encounter are not configured to use this mode. Some older boards and peripherals may not play nice with S3, sound cards being particularly troublesome.
To tweak power management settings in Windows XP and Vista, open the Power Options applet in Control Panel. The three preset schemes are:
- Turn off monitor and/or hard disks only
- Standby/Sleep mode
- Hibernate mode
While Hibernate mode uses the least amount of power, it takes the longest time to suspend and resume, which involves writing and reading the entire contents of RAM to and from the hard disk (using a file named hiberfil.sys). The more RAM you have, the longer the process takes. On the other hand, the Standby/Sleep mode (S3) uses only slightly more power than Hibernate does, yet its suspend and resume times are virtually instantaneous no matter how much RAM is installed.
A BIOS setting called ACPI Suspend Type, ACPI Suspend State, or something similar controls which sleep state (S1 or S3) Windows uses. Many systems are set to S1 by default, which keeps the CPU and RAM powered. Enter your BIOS, navigate to the Power Management menu, and change the ACPI Suspend setting to S3, which cuts power to the CPU and RAM. The screen shot on the first page shows this setting on a Phoenix/Award BIOS. Enable any settings labeled 'USB KB Wake-Up From S3' (the wording varies), and set the Power On Function to Any Key to let the keyboard and mouse wake the PC from standby.
Change Settings to Conserve PC Energy
Depending on the Advanced Configuration and Power Interface (ACPI) settings in your PC's BIOS, the machine may be running up your energy bill even when you're not using it. Click the icon below to see our chart describing different levels of power consumption.
|Change Settings to Conserve PC Energy|
|Depending on the Advanced Configuration and Power Interface (ACPI) settings in your PC's BIOS, the machine may be running up your energy bill even when you're not using it.|
|PC ACTIVITY||ACPI Global/Sleep State||Windows XP/Vista state||Typical power consumed|
|100 percent CPU/graphics load||G0||Power on||Running||305W|
|3D screen saver||G0||Power on||Running||225W|
|Simple screen saver||G0||Power on||Running||195W|
|Idle; Windows desktop||G0||Power on||Running||195W|
|Monitor and hard drives powered down||G0||Power on||Blank screen||160W|
|Monitor and hard drives powered down, CPU halted, fans and other devices running||G1/S1||Power on suspend (POS)||Standby/Sleep||135W|
|Context saved in RAM, everything except RAM powered off||G1/S3||Suspend to RAM (STR)||Standby/Sleep||10W|
|Context saved to disk (hiberfil.sys), system powered off||G1/S4||Suspend to disk (STD)||Hibernate||9W|
|System powered off||G1/S5||Soft-off||Shut Down||9W|
|System unplugged||G3||Mechanical off||Shut Down||0W|