Hacker News Reader

Comment by b800h | Hacker News Reader

With regards to BiiN, one thing I'm not familiar with was how the serial connection to, say, 80 terminals was handled on a machine like this. If I had 80 Wyse terminals (alas, I only have two), and wanted to hook them up to, for example, a Linux server, how would I go about doing that?

View on HN

Thirty years ago ISA cards with 8 RS-232 interfaces were common, so connecting some 30 or even 50 terminals to a single PC was not difficult. I have used a few such computers for testing various devices with serial interfaces.

Eighty terminals on a single PC might have been more difficult, but by that time the computers were already networked, so it would have been cheaper to just use two PCs than to use some kind of terminal aggregator.

I'm going from 30+ year old memories as an intern, but from what I remember:

Usually the RS232 was just on the terminal side. Somewhere along the path it got converted to twisted pair.

All the twisted pair serial lines congregated in the server room at a punch-down box. Eighteen year old me wasn't allowed to mess with anything past that point, but from what I can remember those lines were concentrated by a multiplexer (mux) and sent on to the minicomputer.

I think you're right. I remember seeing a lot of ads for muxes in the Datamation magazines I read as a kid.

I can't give any details about them, because well, I was a kid, and the details of what they were talking about were beyond me...

Back in the 90's, I remember working on an early ISP system that had a 16 port serial card, each connected to a modem. I forget who produced the card (Digi something?) There were revisions with at least 32 ports.

We moved to terminal servers pretty quick. These were dedicated devices that converted serial to IP (Livingston Portmasters, Xylogics Annex, Telebit Netblazers are the ones I remember working with.)

You'd use a terminal server between the terminals and the linux box.

DECserver was a popular one back in the day.

https://en.wikipedia.org/wiki/DECserver

These days it might be more economical to just have something like a Raspberry Pi attached at each terminal. Then the connections to your network could all be wireless.

We didn't always use terminal servers in college. There was a cluster of 3B2s, and two were accessible to students from the terminal room. There were probably 40-50 terminals in the room, and I believe they were each hardwired to either "earth" or "wind". I don't know about the connectors or cabling which achieved that, because the servers were located on another floor of the building. But we were definitely hardwired in.

The rest of the university had general-purpose terminal rooms that used port concentrators. These had a rudimentary CLI that enabled the user to specify a resource to connect to, so it was sort of a circuit-switch deal. Among the resources were VAXen running BSD, VMS machines, and Annex boxes which could be used for TCP/IP connections across campus, or to the outside world. These Annex boxes were also frontends for dial-up users coming in over modems.

The BiiN systems supported RS-232, RS-422, and TTY current loop. I assume you plugged a serial interface board into the system that provided multiple serial ports. But it might have been an external terminal concentrator (or establishment controller in IBM lingo) that hosted the terminals.

I'm still unclear on this - I notice from online that Linux, for example, supports up to 256 TTY devices by default. How might one go about actually physically hooking up that many devices these days? Is a terminal concentrator still available?

In the mid 90’s we used Cyclades multi-port serial cards to do this. These were PCI cards that connected to one or more breakout boxes that contained (in our case) 16 RS-232 ports each. We had 48 total ports connected to a 60mhz Pentium with 32MB of RAM.

This was a decidedly low budget solution, even at the time. There were also commercial offerings from vendors like Cisco and Livingston that provided a terminal server in a dedicated appliance form factor.

edit the breakout boxes look like this: https://149707953.v2.pressablecdn.com/wp-content/uploads/imp...

Here's an example of a PCI card that supports 16 RS-232 devices: https://www.amazon.com/StarTech-com-PCI-Express-Serial-Card/... (not an affiliate link)

Back then there were dedicated boards with large numbers of serial ports. These days you can get PCI(e) serial boards with, say, 16 serial ports.

Personally, I'm using a Commodore A2232 seven port serial board in my Amiga 4000, which has its own 65CE02 CPU to offload work from the main CPU.

What are you using it for? When I was a teenager, I dreamed of getting one of those boards so I could have a multi-line BBS on my Amiga!

I use it to have serial consoles on a number of other machines for remote administration. The sessions get started automatically on boot with tmux and cu, so it's very convenient and easy - much easier than having a ton of USB-serial adapters hanging off of a newer machine.

If you asked me to do it, I'd probably see how many serial/USB adapters I could plug into how many USB hubs attached to a single box. I can't see any reason it wouldn't work, and the parts are cheap enough, and not even particularly obscure. I suspect the failure point would be something in the stack not expecting to have to operate like that and having insufficient performance, but this is all speculative.

Perle continues to make the IOLAN device concentrators (they were Chase brand when I used them in the 90s). Today they’re marketed as “device servers” for connecting console ports on embedded devices to IP networks but you could still serve dumb terminals from them just fine.

16 port isa cards were a thing. apparently they are still made. not fond memories.

DEC or IBM terminal servers. When I was an intern, we migrated ~45k terminals from the legacy serial to IP.

Reply on news.ycombinator.com