Advanced Power Management
The Advanced Power Management (APM)
Specification defines the following power states.
Ready
In the ready state, your computer or device is fully powered
up and ready for use. The APM definition of Ready only
indicates that your computer or device is fully powered on,
it does not differentiate between active and idle
conditions.
Standby
Stand-by is an intermediate system-dependent state which
attempts to conserve power. Stand-by is entered when the
central processing unit (CPU) is idle and no device activity
is known to have occurred within a specific period of time.
Your computer will not return to ready until one of the
following events occur:
A device raises a hardware interrupt.
Any controlled device is accessed.
Suspended
The Suspended state is a computer state which is defined to
be the lowest level of power consumption available that
preserves operational data and parameters. The suspend state
can be initiated by either the system Basic Input Output
System (BIOS) or the software above the BIOS. The system
BIOS may place your computer into the suspended state
without notification if it detects a situation which
requires an immediate response such as the battery entering
a critically low power state. When your computer is in the
Suspended state, computation will not be performed until
normal activity is resumed. Resumption of activity does not
occur until signalled by an external event such as a button
press, timer alarm, and so on.
Hibernation
Windows XP has
built-in support for hibernation (OS-controlled ACPI S4
sleep state). Hibernation saves the complete state of the
computer and turns off the power. The computer appears to be
off. This is the lowest power sleeping state available and
is secure from power outages.
When you resume from a hibernated sleep state, the BIOS
performs the normal POST, and then reads the hiberfile that
was created to save the computer state. The computer returns
to the last state it was in before the computer entered
hibernation mode. Hibernate mode reduces start time.
Note that when you service the computer, make sure you shut
down the computer instead of using hibernate mode.
Windows XP supports Hibernate capabilities (ACPI S4 sleep
state). Windows XP S4OS Hibernate is available on new
computers and upgrades that meet the requirements for the
correct video drivers and no VXD audio drivers.
S4 is the hibernation state. It is very close to the APM
Suspend to Disk state.
Hibernation Requirements
Computer must support APM 1.2, or ACPI.
A paging device that supports D3 (note - certain SCSI
configurations do not support this).
WDM audio.
No legacy capture devices connected.
WebTV for Windows is not installed.
Non-ICS Host (client is OK).
Off
When in the Off state, your computer or device is powered
down and inactive. Data and operational parameters may or
may not be preserved in the Off state.