Device power states D1, D2, and D3 are the device sleeping states.

D1 and D2 are intermediate sleeping states. Many classes of devices do not define these states. All devices must define state D3.

Device Power State D1

Device power state D1 is the highest-powered sleeping state. It has the following characteristics:

Power consumption

Consumption is less than in the D0 state but greater than or equal to that in the D2 state.

Device context

In general, device context is preserved by the hardware and need not be restored by the driver.

Device driver behavior

Drivers must save and restore or reinitialize any context lost by the hardware. Typically, however, devices lose little context upon entering this state.

Restore time

In general, the time required to restore the device to D0 from D1 should be less than restoration from D2 to D0.

Wake-up capability

A device in state D1 might be able to request wake-up.

To minimize the user's perception of delay, restoring a device to state D0 from D1 should incur the least possible delay. Minimizing delay in the state transition is more important than reducing power consumption.

Device Power State D2

State D2 is an intermediate sleeping state with the following characteristics:

Power consumption

Consumption is less than or equal to that in the D1 state.

Device context

In general, most device context is lost by the hardware.

Device driver behavior

Device drivers must save and restore or reinitialize any context lost by the hardware. A typical device loses most context when it enters D2.

Restore time

Restoring the device from D2 to D0 takes at least as long as restoring the device from D1 to D0.

Wake-up capability

A device in state D2 might be able to request wake-up.

In state D2, power consumption drops to the lowest level from which drivers can recover in a reasonable amount of time, that is, without a delay that most users would find noticeably slow for a device of that type. While the priority for state D1 is the user's perception of delay, the priority for state D2 is power conservation. As a result, the restore time from state D2 to state D0 typically exceeds that from state D1 to D0. In state D2, for example, reduced power on the bus might cause a device to turn off some of its functionality, thus requiring additional time to restart and restore the device.

Many classes of device do not define this state.

Device Power State D3

State D3 is the lowest-powered sleeping state. All devices must support this state. It has the following characteristics:

Power consumption

Power might have been fully removed from the device and/or from the system.

Device context

The device driver is solely responsible for restoring device context. The driver must preserve and then restore device context or must reinitialize the device upon transition to a different power state.

Device driver behavior

The device driver is solely responsible for restoring device context, typically from the most recent working configuration.

Restore time

Total restore time is the highest of any of the device power states.

Wake-up capability

Devices in state D3 cannot wake a sleeping system.

In state D3, power has been completely removed from the device or only minimal trickle current is available. Drivers and hardware must be prepared for the absence of power. When power is restored, the operating system applies any necessary hardware-reset signals. To return the device to the working state, the device's drivers must be able to restore and reinitialize the device without depending on the BIOS code being run.

The power manager might remove system power from the parent of any device that enters D3.

All classes of device define this state.