It depends on the era.

Earlier: one PC per user, shared file system using a Novell network. Later: multitasking OS (Desqview, OS/2) or BBS software that natively supported multiple users (like MajorBBS.)

I ran a BBS on an Amiga for a while. The OS natively supported multitasking, but I only had one line. At least I could log in the same time as a user...

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daneel_w 6 hours ago | parent [-]

The older brother of a friend of mine in the 90s was the co-sysop of one of Sweden's largest "elite" BBSes at the time, Farout BBS. I got to tag along to the sysop's apartment once and see the setup, which was an Amiga 2000 with 3 active nodes and available serial ports for a total of 7 nodes, though the sysop hadn't gotten around to get more telephone lines wired to his apartment.

	▲	icedchai 6 hours ago \| parent [-]
		awesome! getting more phone lines into a residence could be a pain. I knew a guy who had an 8 line BBS in his (parents', actually) basement. Getting more was difficult because they were "out of facilities" and he had to move it to an office.