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OnNow Power Management Initiative (Win98)
An Always ON PC feature that
allows a PC to be turned on by external devices. Implementing the Advanced
Configuration and Power Interface (ACPI) in newer PC motherboards, the PC
can be placed into a sleep mode that uses virtually no power until it is
OnNow is based on the ACPI power
management scheme. In order to understand how OnNow works and what role
ACPI plays in this, we will first explain some concepts of ACPI.
Under ACPI, there are 4 distinctive
The working state.
The sleeping state.
The softpower off state and
The mechanical off state.
The G1 state is where OnNow plays its
part. The G1 state contains 4
distinctive sleeping modes S1, S2,
S1: (standby 1) low latency (= quick to wake
system and CPU clocks are stopped, system context is still in its original
S2: (standby 2) low latency
system and CPU clocks are stopped, CPU and cache are powered off and their
data is placed into the memory.
S3: (suspend-to-memory = OnNow) low latency
All board components except the memory are powered off, CPU and cache data
are placed in a reserved area of the memory and retrieved after wake-up.
S4: (suspend-to-disk) high latency
All board components are powered off, CPU/cache/memory data are placed on
the hard disk and retrieved after wake-up.
The OnNow state requires the Motherboard to be able to switch off the
power to all onboard components except the memory. Current Motherboards do
not have this separation of onboard power supply. OnNow ready Motherboards
will therefore require a more complex design for the Motherboards Power
Supply. The PC System Power Supply will also need to support OnNow in
order to make suspend-to-memory (STR - Suspend To
Boot-Fast Resume for the Windows Platform:
Design Goals for WinXP
on a typical Consumer PC are:
- Boot to a useable state in a total
of 30 seconds
- Resume from Hibernate (S4) in a
total of 20 seconds
- Resume from Standby (S3) in a
total of 5 seconds
Boot and resume times are measured
from the time the power switch is pressed to being able to start a
program from a desktop shortcut.
and Power Management: ACPI / Power
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- Posted 11/14/2001;