suppose power is scarce, like in airplane, and what the laptop is being used for is not at all taxing on the machine’s resources, like reading a book or writing texts. In this situation I think that one of the ways to save power would be to shut down hard drive and have the machine run purely on RAM. So the idea is that we turn on the machine, load all the needed data from disk to RAM, turn off the disk and work using RAM. If there is anything to save along the way (a big if, especially if I am just reading) I save it to flash.
Can Windows OS be told to do so? How about the various *nix variants intended for the desktop/consumer?