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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 "awakened."

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 power states:

../images/bullet2.gifG0: The working state.
../images/bullet2.gifG1: The sleeping state.
../images/bullet2.gifG2: The softpower off state and
../images/bullet2.gifG3: The mechanical off state.

The G1 state is where OnNow plays its part. The G1 state contains 4 distinctive sleeping modes S1, S2, S3, S4.

S1: (standby 1) low latency (= quick to wake up)
system and CPU clocks are stopped, system context is still in its original state

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 RAM) work.

  1. Fast Boot-Fast Resume for the Windows Platform:

    Design Goals for WinXP on a typical Consumer PC are:

    1. Boot to a useable state in a total of 30 seconds
    2. Resume from Hibernate (S4) in a total of 20 seconds
    3. 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.

  2. OnNow and Power Management: ACPI / Power Management.
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Web Development, Gill Boyd & Team - Posted 11/14/2001; Updated 04/25/2008