Switch Windows XP to hibernation mode

I saw an article, "Hibernation is an outstanding property of Windows. When user switches Windows to the Hibernation mode, it copies the data of RAM to the hard disk and switches off the power supply and whenever the user switches to the general mode, all the data from the hard disk gets reloaded on RAM. It’s an extremely efficient way to keep the computer system on without consuming electricity."
Great! How to switch Windows XP to hibernation mode?
