Special software that's built into laptop computers and some newer desktop PCs and monitors. Power management is designed to cut the power supply to a device or peripheral when it's not being used. For example, if the PC has not been used for 10 minutes, the power management software might cut power to the disk drive, which normally spins constantly, or to the monitor. As soon as you hit a key or move the mouse your computer wakes up again. In a laptop, it's a good way of conserving the battery power.
