Device States (D-States)

Device states occur in the global system G0 working state. They were defined to enable device vendors to design ACPI-compliant products, so that operating system that support ACPI, like Windows XP, can manage the devices. There are four D-states, but vendors can choose not to implement all states.

D0 State

• In this state, the device is operating at its full power and full functionality.
• Example : A DVD-ROM drive in active use.

D1 State

• The device can choose to discard its context.
• However, the bus connected to this device should not do anything to cause the context loss in the device.
• Power consumption is lower than the D0 state, as some working units in the device will shut down.
• Example : After idling for some time, the laser in the DVD-ROM drive will automatically turn off, but the drive controller will still be active.

D2 State

• It is similar to D1, but the bus is free to some power management, like lower the current and voltage.
• This can save more power, but it will take a longer time to wake up from the D2 state.

D3 State

• The device in this state can be completely turned off.
• Maximum power saving is achieved.
• Wake-up time is the slowest among all D-states.

D-State Examples

Example 1 - Hard Disk Drive Power Management Policy

Example 2 - Graphics Card Power Management Policy

* DPMS : Display Power Management Signal, defined by Video Electronics Standard Association (VESA)