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Normally when you call a POTS phone that's already connected to someone else, you'll get a busy signal. How did Bulletin Board Servers allow multiple users to dial-in simultaneously? Would there be a limit on how many users could be connected?

TreyK
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2 Answers2

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ISP's that supplied dial-up back then just had banks of telephone lines and modems so that multiple users could dial in simultaneously.

There was most certainly a limit on number of callers (= number of modems and lines they had). I do recall getting up early on weekend mornings with my repeat dialer and let it run until it connected.

Very simple and low grade technology but it worked.

Reference: https://en.wikipedia.org/wiki/Internex_Online

That was the dial-up system I used in the later 1980's

John
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    I saw a minicomputer around 1974 that was used in a regional (South West England) university library book reservation and cataloguing system and it had (if I remember correctly) 4 acoustic couplers with ordinary phone handsets sitting in them. At the other end would be terminals likewise equipped. So 4 users on line at any one time. – Michael Harvey May 16 '20 at 23:44
  • My answer above was for 1983-1984 Internet and Bulletin Boards. There were about a dozen or so users simultaneously – John May 16 '20 at 23:46
  • Would this require BBS servers to be colocated at the ISP? If not, how would multiple lines be run out to the customer that all map to the same phone number? – TreyK May 17 '20 at 01:48
  • Back then, the ISP had office space that provided the telephone system that had one number that multiple lines could answer. Co-location was not a concept (at least not frequently used) back then. This was some decades back. The company also had the servers to supply BBS and some Internet as time went on. They provided email as well with their servers – John May 17 '20 at 01:51
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    @TreyK+ to be concrete, one number (dialed by all callers) can easily map to multiple lines, each of which normally had a separate number used for billing but not dialling; see https://en.wikipedia.org/wiki/Line_hunting . This was fairly common for businesses receiving high-volume voice calls as well as BBS and small ISPs receiving data calls that were typically lower volume but longer (often several hours while most voice calls were only minutes). Meta: this type of Q might be better on retrocomputing.SX. – dave_thompson_085 May 17 '20 at 03:15
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The the 80's you could implement roll-down lines with either your phone company, or install a local PBX in your building that also did roll-down. So, if the primary line was busy, the next number or extension on a PBX would ring.

Then it was a matter of multiple machine hardware (Computer, Modem, etc) - you could do one environment per phone number. Eventually things evolved to allow for multiple phone lines/modems to a single computer if the BBS software was self-multitasking... or,

There were time-slicing solutions like Desqview, DoubleDOS, PC/MOS, etc. (again all of these solutions were pre-Windows 95/NT.) and eventually some of us (Sysops and BBS Authors) started migrating our software to Windows and Linux - to cut-down the cost of all the hardware, and run multiple "nodes" on a single computer.

(*) Note for those who care, there are some of us (BBS Authors) who are still actively developing solutions for the BBS community ... I am doing the rewrite of ProBoard BBS, still keeping a 16/Bit DOS build on the to-do list, along with support for native TCP/IP based solutions. An FYI, the 16/Bit DOS builds work with tricks like DOSBox (which allows us to set serial ports as Virtual modems, and allow DOSBox to do the COMPORT<->TCP proxy for us. And another solution is NetSerial and/or Net2BBS from pcmicro.com - Mike is active in helping people convert their modern Windows systems to work with older BBS applications.

Ozz Nixon
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