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?
Best Answer
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.