Sometimes called Remote Wake-up, Wake on LAN is technology that allows someone to turn on a network computer remotely by sending a special data packet (called a Magic Packet). Even if the computer is turned off, the network adapter is still "listening" on the network, so when the special packet arrives, the network adapter can turn on the computer.
Wake on LAN is mainly used by system administrators to perform computer maintenance tasks remotely. The computer receiving the Magic Packet must have a motherboard, network adapter, adapter driver, and computer basic input/output system (BIOS) that work with Wake on LAN.
In Windows 7. Wake on LAN is enabled by default in desktop computers but disabled in laptops. For more information, go to the Microsoft TechNet article Power Management for Network Devices in Windows 7.