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.
“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.”
I wrote the software for a breakout box that could handle 128 serial ports. It was an ISA backplane with an industrial 286 computer and multi-port serial cards. This was our solution for a MajorBBS system.
The BBS software would have to timeslice between all the cards handling each IRQ, then poll the card details to see which ports needed service.
GalactiComm eventually came out with their own around 1993 that could go out to 255 serial ports and did not require the 286 processor.
By the mid-90’s, Livingston PortMasters were the preferred way to aggregate serial connections, which quickly gave way to USR TotalControl.
[^1]: e.g. https://en.wikipedia.org/wiki/Diversi-Dial
That's because she doesn't know what she's talking about.
I knew a couple of local DOS BBSes that ran multiple lines with PCBoard under DESQview.
PRI was a huge step. The "individual modem" days were a mess. Each modem had a serial cable, phone line, and power brick. I remember doing some maintenance in one of the POPs. There were at least 100 modems, stacked on a cheap plastic shelving unit. The shelving unit was sagging from the weight and heat of all the modems.
This early POP was haphazardly built, so no cable management. I remember a river of phone cables coming out of the wall. The power bricks were also crazy. We had power strips 2 or 3 levels deep, making it a hazard to even get behind the rack without tripping on something.