By Iljitsch van Beijnum | Published: September 21, 2007 - 01:10PM CT
http://arstechnica.com/journals/apple.ars/...eeping-macs-lieQUOTE
Some people let their computers run 24/7, but you can save some money on electricity by turning your Mac off or putting it to sleep when you don't use it. This is especially true for a secondary computer that you don't use all the time. However, sometimes it's annoying to have to walk over and turn on or wake up that computer when you need it. As luck would have it, there's an easier way to do it—if your computer is connected to your local network through wired Ethernet, that is.
On most Macs, if you go into the System Preferences and select the Energy Saver, under Options there is a checkbox for "Wake for Ethernet network administrator access." That network administrator could be you! Enabling this option means the computer enables the ability known elsewhere in the industry as "wake on LAN." The Ethernet adapter will now stay powered up and wake up the rest of the computer when it sees a "magic" packet.
Apple's Remote Desktop will send those packets, but you can also download a free utility like WakeOnLan. There are also tons of perl and python scripts that will do the same. Note that the original purpose for this mechanism was to start up a computer that was turned off. Macs don't do this, they'll only wake up from sleep.
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Unfortunately, Apple's Airport Extreme base stations won't turn packets coming in from the Internet into Ethernet broadcasts, so if you have one of those, you'll have to let sleeping Macs lie.
