Commercial ethernet switches weren't a thing until 1990 (Kalpana), and 100Mb ethernet is from 1995. So, yeah, a lot of ethernet in the late 90s was 10Mb. It's still a thing today in some embedded applications, and switches still support it.

Most any switch that supports 10GBase-T will only auto-negotiate down to 100Base-T, and some of them will only go as slow as 1GBase-T.

10Base-T was an upgrade over 10Base-2 and 10Base-5 (AUI), but the latter were more popular in the early 80's.

Well, yes...since 10base-T wasn't a standard until 1990[1] it's a pretty easy guess it was less popular a decade before.

[1] https://standards.ieee.org/ieee/802.3i/1068/

I guess I hadn't stepped back to think about the difference between computer ethernet and switched ethernet. I _do_ remember hubs, though, so it should have occurred to me that we didn't have switching on day 1.