How does a computer update the time automatically without power?
Inside a computer is a BIOS which is a small chip that holds essential information for the computer to start up, including the time. While the computer is plugged in, a small battery is being charged inside the computer, so if you unplug it, the battery takes over and the clock stays correct.The battery lasts a very long time, but if you were to unplug the computer and leave it long enough, the time would be forgotten and you would need to set it again next time you turn the computer on.