alt Hacker NewsThat's more useful. A big question is how much is really turned off in a computer waiting for the wake-up packet. "The power to the Ethernet controller must be maintained at all times, allowing the Ethernet controller to scan all incoming packets for the Magic Packet frame". So the full network controller is still alive. There's not some tiny Magic Packet detector hardware running off a rechargable coin cell or something, with the main power supply turned off. At least not in the original design.
A lot of sleep modes leave more running than you'd expect.
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pjc50 • today at 7:42 PM
It probably is done in hardware; I expect you'll end up with the TX side of the Mac/phy powered down but all the receive running. Miliamps at most.
The Ethernet cards that wait for WoL packets use the "+5 V Standby" supply voltage, which is available on the PCIe slots, coming from the ATX power supplies.
"+5 V Standby" is provided by a separate voltage regulator, which continues to work even when the PC, including the rest of the ATX PSU, is shut down.
"+5 V Standby" typically can provide up to 2 A, i.e. up to 10 watt, though some old PSUs may be able to deliver only up to 5 watt and some of the bigger ATX PSUs may be able to deliver up to 15 watt.
Besides supplying the Ethernet cards, to enable WoL, "+5 V Standby" can be used by the USB ports if configured so in BIOS, to enable waking the PC with the keyboard, or to enable charging from USB even when the PC is shut down.