Some details/speculation from the original thread here: https://news.ycombinator.com/item?id=30098186

“as modems got faster, supporting 16 modems on a single machine became impossible, and it was often cheaper to buy a new commodity desktop PC rather than a much more expensive machine with a 16-port serial card capable of handling the IO.”

Even the Apple II had multi-line BBSes[^1], so I'm not sure about her assumption.

[^1]: e.g. https://en.wikipedia.org/wiki/Diversi-Dial

Even for a standard PC, you could buy a 16 port serial card and hook it up to 16 modems, either discreet devices or the dedicated ISP kit which might support dozens of incoming calls (possibly on a single bearer) via various means. Telebit netblazers and then ascend maxs were common in those days.

I'm fairly certain you are correct. I remember the MajorBBS could handle multiple lines on its own.

I knew a couple of local DOS BBSes that ran multiple lines with PCBoard under DESQview.

A guy who was local to me, when I was a kid, wrote multi-user BBS system (called "MUBBS" originally-- I don't remember what the name was changed to later) in Turbo Pascal that had a preemptive multitasking loop running in x86 real mode to handle multiple lines simultaneously. The coolest part was the console was just a "line" so you could logon to the board and interact while somebody was online with the BBS, too. Most other DOS BBS packages were only available for the SYSOP or the caller individually.

Edit: Ugh... I'm gonna have to go back to floppy images to find it. There's a "MUBBS" for Mac from 1992 showing up in search engine results but that's not the one I'm thinking of. It was more like 1989 or 1990.

That assumption feeds into the moral of the post and its followup

Serial ports are a fun thing to learn about, computers had more than one. Now with USB, computers can have many serial ports.