PC’s having the “Green PC” specification offer a power management section in the BIOS. This is used to control the various power saving features of the PC. The idea is that, as longer periods of time go by without any user activity, the system is gradually put to sleep. This is done in such a way that when user activity is detected, it all must power back up as quickly as possible. This is done via a power management unit (PMU) that monitors interrupt signals through an interrupt events detector. BIOS options help in this, but your operating system also plays a key role.

There are several modes in which a PC can be in:

• Dozing slows the CPU down only, to around half speed.


• Standby shuts down HD and video, or CPU and SCLK (depends on the chipset).


• Suspend shuts down all devices except the CPU.


• Inactive stops the CPU, slows the SCLK and powers down the L2 cache.


• HDD Power Down just shuts down the hard disk.

There are several power management standards:

• APM, or Advanced Power Management
  Devised by Intel/Microsoft. This must be active if you want to keep the time and date when the system is suspended. APM is responsible for shutting the system down when quitting the operating system.


• ATA, or AT Attachments Specification
  For IDE drives. Some ATA compliant devices provide Spin down facilities.


• DPMS, or Display Power Management Signaling
  Monitors and cards conforming to this are meant to be matched, as signals are sent between them to put the CRT into various low power states. This requires BIOS Support.


• ACPI, or Advanced Configuration and Power Interface
  Developed mainly by Intel, Microsoft and Toshiba. This will allow desktop PCs to have instant on, and be better for voicemail and household device control, as peripherals can be turned off as well as the main system unit.

The BIOS Settings

BIOS settings for power management are included on almost every motherboard that is sold today. The options themselves vary, but they are also usually pretty obvious based on their wording. So, I will only address a few basic options here.

• Power Management
  The level of power management can be set. Disable if you don’t want any of it. You can use min or max settings that are pre-determined, or set to “User Define” to specify.


• PM by APM
  Used to either enable or disable APM power management.


• Video Off
  Either disable or set to DPMS. You can also just go to blank screen.


• PM Timers
  Used to set the waiting period before the PC starts shutting down its components. Disable to make sure this doesn’t happen. Or you can set up times for things such as HDD power down, doze mode, and suspend mode.


• Soft-on by Power BTTN
  Controls whether the PC shuts off immediately after hitting the power button or delaying a few seconds.