It’s crazy that the Ethernet chips consume more power (presumably - because of the heat) than the processor in the computer. How is driving 25Gb/s such a hot task compared to driving multiple 40Gb/s Thunderbolt ports?

> It’s crazy that the Ethernet chips consume more power (presumably - because of the heat)

The NIC in this setup was released 12 years ago. It's built on a very old process.

As I understand it, it takes a bit of anger to get electromagnetism to wiggle that fast over copper. Imperfect transistors using their full operational envelope to control a sort of chaotic thing? Fields and stuff.

They’re not that bad, but even a couple watts of power with no way to dissipate is going to get hot enough to burn you. Forced air cooling over a heatsink is really effective. 15W under load is much lower than a high end desktop CPU that can pull 150-200W.

See also NVMe drives? They draw enough idle power to drain a laptop battery overnight, and will easily hit 60+C in a bad enclosure. That’s only a 10Gbps module. The USB4 enclosures are all heatsink.

A Mac Studio is over 100 W while a 25G NIC is under 25 W (that's the power limit for a normal PCIe slot).

is 10W a lot of power? I absolutely don't believe the cpu is using less than that while pushing 25Gb out

you can look up the rated power use of a connectx4 card, they do a lot of offloaded computation, too

Maybe the NIC does a lot? In past experience, a whole Xeon CPU couldn't keep up with a 10gig NIC if it was sending/receiving min-size UDP packets. Even with Intel DPDK iirc.

Something like 5 percent of AI datacenter usage is just optics.

It's distance. 25GbaseT is good for 30m+. Thunderbolt is good for 1m without active cables. Making the much more rugged signal is a much more intense job.

And your computer already speaks the PCIe and thunderbolt. It has that probably on CPU. Here we have to receive USB, convert it to Ethernet. On much less up to date process nodes than your CPU.

Third, until very recently for even 10Gbit it meant using a usb4<->pcie bridge chip which itself was hot, to provide a generic pcie connection, which then talked to a conventional network chip, so it was a double hop: USB <-> pcie <-> nic. I don't know if 25Gbit to USB direct convert is available yet but we've seen a wave of vastly cheaper 10Gbit adapters come out that are single chip USB<->nic, probably not pcie at all, that are much much cooler. 25Gbit is probably still not here yet, maybe?

Ethernet is isolated through transformers on the physical layer and they're always sinking power. Thunderbolt is just pushing current directly through.

With ethernet it's for lots of reasons but a big one is not creating ground loops between distant equipment. If you didn't isolate the network cable would be sinking potentially amps of current between distant devices and that just isn't sustainable. You don't have this problem attaching USB between two devices.