For those of us who don’t know, how does it save power vs a 1gbe running at low throughput?

> how does [100BASE-TX] save power vs [1000BASE-T] running at low throughput?

100BASE-TX uses just two pairs (lanes), one for sending and one for receiving. 1000BASE-T uses all four pairs, for both sending and receiving. Therefore, a 100BASE-TX interface that's only receiving needs to power up one pair. A 1000BASE-T interface needs to power all four pairs all the time.

I recall reading about some extensions that allow switching off some of the pairs some of the time ("Green Ethernet"), but I think that they require support on both sides of the link, and I'm not sure if they are widely deployed.

100M also needs much less signal processing, and at lower speed, than 1G.

10M is even simpler, to the point that even a fast MCU can bit-bang it.

My only annoyance with "Green Ethernet" things is that often they seem to work poorly.

The dedicated machine I still keep around for Windows things has two onboard 2.5GbE ports. It will apparently sometimes, even with all power saving features turned off, randomly negotiate down to 100 mbit if I leave the machine alone for a bit, and then stay at that speed forever unless I manually reset the link after wondering why transferring large amounts of data is bottlenecking severely.

I assume it is for wake-on-LAN. This of course requires the NIC being powered on while the system is sleeping. Lower bandwidth mode = less power draw.

TVs too.

And PoE security cams.