That'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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adrian_b 4 hours ago | parent | next [-]

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.

	▲	VorpalWay 21 minutes ago \| parent \| next [-]
		I have measured the powered off energy usage of my desktop computer at the wall, and it hovered about 5-6 W (resolution of the power meter was just whole watts). That would be split between losses in the PSU and WoL, and possibly other circuits. But I don't have any other such wakeups enabled (but that doesn't mean that the motherboard is designed super well to disable it fully if not needed). Turning off WoL made a difference of about 2 W (meter hovered around 3-4 W). One thing I noticed is that if I connect to a gigabit upstream port, that the connection drops to 100 mbit/s when the computer is off, but if I connect to a 2.5 Gbit port, it stays at full speed. This is based both on LEDs on the connector as well as the OpenWRT dashboard on the router. If it made a difference it was too small to reliably measure with my simple meter. If it makes a difference (potentially does for conversion losses I would guess), this is on 230 V mains.
	▲	jonah-archive 3 hours ago \| parent \| prev [-]
		Exactly this. Many modern PHYs also integrate 802.3az (energy-efficient ethernet, a subset of Green Ethernet) but it's not super common. I also finally found this old page of using an old dev board to construct a WoL listener for a mobo that didn't support it -- might be an interesting read for the curious: https://web.archive.org/web/20140525022112/https://hackingbe... > In this script a fifo is created where the output of tcpdump is dumped. For whatever reason tcpdum \| grep was not working properly, and would have a “miss” rate of about 50%. So tcpdump output is dumped in the fifo: > > tcpdump -i eth1 2>&1 \| tee > /tmp/tcp_wol.fifo & > > and it’s grepped in a loop, when the magic packet (see http://en.wikipedia.org/wiki/Wake-on-LAN) is found , a led is triggered, thus powering-up the computer (with a driver and relay, will come back at this).

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pjc50 3 hours ago | parent | prev [-]

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.