Hardware Reference
In-Depth Information
setting is called
ACPI suspend mode
, and ideally you want it set so that the system will enter what is
called the S3 state. S3 is sometimes called
STR
for
Suspend to RAM
. That has traditionally been the
default setting for laptops; however, many if not most desktops unfortunately have ACPI suspend
mode set to the S1 state by default. ACPI S1 is sometimes called
POS
for
Power on Suspend
, a state
in which the screen blanks and CPU throttles down; however, almost everything else remains fully
powered on. As an example, a system and LCD display that consumes 250W will generally drop to
about 200W while in S1 Sleep; however, the same system will drop to only 8W of power
consumption in the S3 (Suspend to RAM) state.
When the system is set to suspend in the S3 state, upon entering Sleep (either automatically or
manually), the current system context is saved in RAM and all the system hardware (CPU,
motherboard, fans, display, and so on)
except
RAM is powered off. In this mode, the system looks as
if it is off and consumes virtually the same amount of power as if it were truly off. To resume, you
merely press the power button just as if you were turning the system on normally. You can configure
most systems to resume on a key press or mouse click as well. Then, instead of performing a normal
cold boot and full restart, the system almost instantly powers on and resumes from Sleep, restoring
the previously saved context. Your OS, drivers, all open applications, and so on, appear fully loaded
just as they were when you “powered off.”
As mentioned, many people have been using this capability on laptops, but few seem to be aware that
you can use it on desktop systems also. To enable this deeper sleep capability, there are only two
main steps:
1.
Enter the BIOS Setup, select the Power menu, locate the ACPI suspend setting, and set it to
enter the S3 state (sometimes called STR for Suspend to RAM). Save, exit, and restart.
2.
In Windows, open the Power Options tool in the Control Panel, locate the setting for the Power
button and change it to Sleep or Stand by.
You can also take advantage of hibernation, which allows you to use the ACPI S4 (STD = Suspend to
Disk) state in addition to S3. ACPI S4 is a lot like S3, except the system context is saved to disk (in a
file called hiberfil.sys) instead of RAM, after which the system enters the G2/S5 state. The G2/S5
state is also known as Soft-Off, which is exactly the same as if the system were powered off
normally. When you power on from Hibernation (S4), the system still cold boots; however, rather
than reloading from scratch, Windows restores the system context from disk (hiberfil.sys) instead of
rebooting normally. Although hibernating isn't nearly as fast as S3 (Suspend to RAM), it is still much
faster than a full shutdown and restart and works even if the system loses power completely while
suspended. Windows XP and earlier allows you to place a system in Standby (Sleep) or Hibernate
modes, while Windows Vista and later has Sleep, Hibernate, and Hybrid Sleep modes. Hybrid Sleep
is a combination of sleep and hibernate, where the system state is saved both in RAM and to the hard
disk as a backup. Hybrid Sleep is the default Sleep function setting for desktop systems, and because
of the extra time to create the hiberfil.sys file it unfortunately makes the system take just as long to
Sleep as it does to Hibernate. To speed up the Sleep mode functionality in Windows Vista and newer,
you can disable Hybrid Sleep.
Finally, to make the system Sleep automatically, you can change the Windows Power Scheme settings
to put the system in Sleep mode after a time duration of your choice. This allows the system to
automatically enter Sleep mode after the preset period of inactivity (I usually set it for 30 minutes to
an hour) has elapsed.
