Back when I was starting out with micros, 300 baud modems were of course around, and they always made a point to mention that they also supported the older 110 baud standard. 9600 baud modems were available (and that used to still be the limit on fax machines for a long time thereafter I believe) but cost the Earth and were business techology. 1200 baud was available, and the BBS around here were about half and half 300/1200 (and the 1200 supported the slower speeds). Next thing I knew, 2400 baud, then (for about a half second) 4800 baud (Motorola offered an upgrade to us haughty 2400 baud owners), then 9600 for the home. The phone lines around here wouldn’t handle anything over 1200 baud (on a good day), too much noise.
Z-modem protocol was a necessity for transfers, mainly because CPUs would only do one thing at a time online, and downloads took a while; Z-modem would pick up where it left off if there was an interruption.
Then the 14400 came out.
Then, 28800.
Then, 37something (I don’t feel like doing the math or looking it up).
Then, 56K, which only runs at something like 48K anyway.
It’s interesting, because in the mid-1980s in one of the now-long-defunct computer monthlies (either Personal Computing or Popular Computing, I think) the cover story was about the AT&T proposal for the 56K protocol over the existing phone network. Took ten years, or a bit more.
It looked something like this
lol.
I was very happy to finally get the Tandy 386 home.