In my book Upgrading and Repairing PCs I've advised people to turn off
systems when they are not going to be using them for more than a few hours.
However, I must admit that lately I have not been following my own advice. In
fact I rarely turn my systems off anymore (at least not "off" in the normal
sense), and yet if you saw them unattended they sure *look* like they are
off, not to mention that they use the same amount of power as if they are off
What am I talking about? With the improved power management capabilities of
modern hardware, combined with the stability and control features built-in to
modern operating systems like Windows XP and Vista, you can effectively power
your systems off and on almost instantly, without having to go through the
lengthy shutdown and cold boot startup procedures over and over again. I'm
frankly surprised at how few people I see taking advantage of this!
The problem is that most desktop PCs perform a full shutdown procedure when
you press the power button, closing all open applications and shutting down
the OS and system completely. Then when you turn the power back on, they do a
cold boot, reload the OS, drivers and startup applications from scratch,
after which you still have to open any other applications you normally use.
The alternative is much better: that is to have the system save the full
system context (state of the system, contents of RAM, etc.) before powering
off, and subsequently restore this context when powering on.
The key is in the system configuration, starting with one very important
setting in the BIOS Setup, that is setting what is called ACPI suspend to
enter the S3 state, sometimes called STR for Suspend To RAM.. That is the
default setting for laptops, however many if not most desktops unfortunately
have ACPI suspend set to the S1 state by default instead. ACPI S1 is
sometimes called POS for Power On Suspend, a state in which almost everything
remains fully powered on.
When set to suspend in the S3 state, upon entering Stand By (either
automatically or manually), the current system context will be saved in RAM
and all of the system hardware (CPU, motherboard, fans, display, etc.)
*except* RAM will be powered off. In this mode the system will look like it
is OFF, and consume virtually the same amount of power as if it were truly
To resume you merely press the power button just as if you were turning the
system on normally. However, instead of performing a cold boot and full
restart, the system will instantly power on and resume from Stand By,
restoring the previously saved context. Your OS, drivers, all open
applications, etc. will appear fully loaded just as they were when you
Many people use this capability on laptops, but few seem to be aware that you
can use it on a desktop systems as well. To enable this 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. Table 5.29 in URPCs 17th Ed. shows how this
setting appears on most Intel motherboards.
2.) After Windows loads, open the Power Options tool in the Control Panel,
then select the Advanced tab. For laptops - Under Power buttons set "When I
close the lid of my portable computer" to Stand by. For desktops - set "When
I press the power button on my computer" to Stand by.
I also recommend selecting the Hibernate tab, then check the box to Enable
hibernation. This will allow you to use the ACPI S4 (STD = Suspend To Disk)
state in addition to S3. ACPI S4 is like S3, except the system context is
saved to disk (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 will still cold boot, however rather than
reloading from scratch, Windows will restore the system context from disk
(hiberfil.sys) instead of rebooting normally. While this isn't quite as fast
as a warm boot resume from Stand By, it is still much faster than a full cold
boot restart, and will work even if the system had lost power completely.
In addition, I also recommend selecting the Power Schemes tab, and under
Settings for Custom power scheme; When computer is Plugged in; set System
standby to the duration of your choice (I usually set it for 30 minutes).
This allows the system to automatically enter Stand By after the pre-set
period of inactivity has elapsed.
Once these settings are complete, on a laptop you can manually put the system
into Stand By by simply closing the lid, while on a desktop you can press the
power button instead. On both laptops and desktops you can also invoke Stand
By manually by selecting Start; Turn Off Computer...; Stand By.
You can select Hibernation instead of Stand By if you select Start; Turn Off
Computer...; then press the Shift key (causing Stand By to change to
Hibernate); then with the Shift key pressed, select Hibernate.
While using the Shift key to change Stand By to Hibernate is normal behavior,
if you would like the Hibernate option to appear *in addition* to Stand By
without having to remember to press the Shift key, you can apply the
following Hotfix and registry changes:
When you click "Turn Off Computer" on the Start menu, the Hibernate button
does not appear
Besides using these manual methods, remember that the system will
automatically enter Stand By after there is no activity for the pre-set time
you entered under Power Schemes.
Here are some power measurements I made on a test system running Windows XP,
a 3.2GHz Northwood P4 with HyperThreading enabled (overclocked to 3.41GHz),
Intel 865G integrated graphics, 1GB PC3200 DDR RAM, 160GB SATA drive, DVD
burner, etc. These measurements are for the system unit only, not including
7W: Powered Off
7W: ACPI S4 (Suspend To Disk) Hibernate
8W: ACPI S3 (Suspend To Ram) Stand By
75W: ACPI S1 (Power On Suspend) Stand By
85W: Powered On, Windows desktop, nothing else open
170W: Running Prime95 torture test (2 instances, 100% CPU/RAM usage)
As you can see from these power measurements, Hibernation consumes exactly
the same amount of power as powering off normally, which is expected since in
both cases the system ends up in the same G2/S5 (Soft Off) state. The 7 watts
of power consumption that remains is due to the standby power used by the
power supply and motherboard, common on all modern systems.
In the ACPI S3 Stand By state, only 8 watts are used, indicating that only 1
watt extra is required to power the RAM over being completely turned off. The
S1 Stand By state is unfortunately not much better than being fully powered
on, as the system consumed 75 watts in that state vs. 85 watts sitting at the
Windows desktop fully operational.
As a stress test, I ran two instances of the Prime95 program in Torture Test
mode (selecting In-place large FFTs), running each instance on a different
virtual core (HyperThreading) to maximize both CPU and RAM usage. This
brought power consumption up to a steady 170 watts. It also caused the CPU to
heat up quite a bit, using SpeedFan to view the temperature the processor
measured only 29C (84.2F) idling at the Windows desktop, but increased to 47C
(116.6F) when running the stress test.
Seasonic Power Meter: http://www.seasonicusa.com/power_angel.htm
Bottom line: Using the ACPI S3 Stand By and ACPI S4 Hibernation states allows
you to take advantage of the advanced features found in modern hardware and
operating systems in order to "power off" and "power on" systems virtually
instantaneously, with virtually no additional power consumption as compared
to being powered off normally. Scott.