Does Disabling a PCI Device in Windows Device Manager Shut Off Power?

Question

Hardware devices can be easily managed in Windows using the Device Manager. I am interested in completely powering off a PCI device (my graphics card, for instance). I am aware that, in Device Manager, a device can be 'Disabled', for which this documentation exists

Disable a device

When you disable a device, the physical device stays connected to your computer, but the device driver is disabled. The drivers are available again when you enable the device. It can be useful to disable devices if you want to have more than one hardware configuration for your computer, or if you have a portable computer that you use at a docking station.

Does "the physical device stays connected to your computer" mean that the device is still powered on? Can this even be done through Windows, or is power management of PCI devices BIOS-related?

Answer 1

After some research, I found this useful information on the MSDN, which pretty much answers the question.

In summary, a device can have various states in terms of its power consumption:

Fully on State: D0
Low Power States: D1, D2, D3hot, D3cold

The difference between the low power states is explained nicely in this subsection of the MSDN article. It appears that when a user hits 'Disable' on a device through Windows Device Manager, the OS follows the instructions of the device driver, which decides which of D1, D2, D3hot/cold lower-power states to put the disabled device in.

D3hot and D3 cold are states that are new in Windows 8, and there are various complications in transitioning between power states that a driver programmer must take into consideration.

Answer 2

Does "the physical device stays connected to your computer" mean that the device is still powered on?

Yes, albeit drawing least possible power - in the ballpark range of a few milliamps (0.2-3 ma). Significantly lower than the normal power range (10ma to .9Amp USB3) were it to be enabled. The minimum power allows windows to communicate with the device.

Can this even be done through Windows, or is power management of PCI devices BIOS-related?

Yes.

Additional Points:

Newer windows versions such as Windows 10 have markedly improved capability for scenarios such as these - because the newer kernels talk better with UEFI BIOS and also can utilize motherboard/device configurations better. Hence, if you are using Windows Vista or earlier, there would be a marked negative difference regarding power savings.

I have some anecdotal evidence to justify - my USB devices were behaving erratically. For example, at times, my internet dongle would not get detected, at other times my mouse tracking was not smooth. But most of these were intermittent issues. It was hard to diagnose that the reason was NOT the device / software / drivers / Windows / motherboard. It was my PSU which was not able to provide sufficient power to all the USB devices. I tried disabling them in Windows, and there was a significant improvement.