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So, I found one of these:

IBM5291

(It's as if it's new, it wasn't ever used, it sat on a bookshelf next to an old CRT monitor, it also has every part).

On the front there's a small gray box with the text

IBM
5291

on it. I tried googling it, but literally nothing useful came up, only pictures from shared folders. No one is writing about it, no one is asking about it on forums, heck, no one even sells one on e-bay or other online markets. The most useful link was from a newspaper archive with a newspaper from '82 mentioning this.

What's this machine and from when? How much is it worth?

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    Side note: the keyboard is amazing though. One of the best mechanical keyboards I ever used.
    – Bálint
    Nov 29, 2016 at 18:10
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    It's a terminal for IBM minicomputer systems like the System/36 and AS/400 (basically anything that can use a 5250-compatible terminal). It has no real use outside that.
    – Joe
    Nov 29, 2016 at 18:16
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    @Joe, I wouldn't be surprised if you could use it as a terminal for a Linux system.
    – Mark
    Nov 29, 2016 at 19:50
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    @Mark: IBM terminals have their own block-oriented protocol, so you can't use them directly on a Linux box, even if you somehow manage a connection on the hardware level (which also uses its own standards, no RS-232 here).
    – dirkt
    Nov 30, 2016 at 7:19
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    @dirkt oh, and I did find a fix the Open Watcom C compiler's installer (which was tripping up on xterm and similar terminals) using it :) github.com/open-watcom/open-watcom-v2/issues/225
    – Wyatt Ward
    Sep 10, 2018 at 15:41

2 Answers 2

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The IBM5291 is one of the IBM5250 series of terminals. It provides a user interface to an IBM minicomputer.

The interface will be by Synchronous Data Link Control (SDLC). The hardware being paired co-ax wire system. This enabled a number of these terminals to be daisy chained to a single port on the host minicomputer.

There are a number of modern emulators around for these terminals, so that you can use, for example, a Windows PC to communicate with your old IBM mini. However, they use virtual network connections as opposed to physical wired connections.

Going the other way - using your terminal to communicate with a modern computer - would require a hardware adapter.

There is a manual for the 5291 available online here that you may find useful. It includes the keyboard pinouts, so you can set yourself a challege to repurpose the keyboard for something else.

What is it worth? Depends if you can find someone with an AS/400 (or similar) who wants an SDLC compatible terminal for historical reasons.

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  • Hmm, I really doubt there are ibm terminal collectors out there.
    – Bálint
    Dec 1, 2016 at 6:47
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    There are people who collect old IBM stuff.
    – Warren P
    Dec 2, 2016 at 2:31
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    It might actually be useful as a console for such a machine, even if you're accessing it through an emulator on a network.
    – ConcernedOfTunbridgeWells
    Dec 5, 2016 at 11:50
  • @Bálint people collect dead insects...IBM terminals don't sound that strange to me.
    – cbmeeks
    Dec 5, 2016 at 19:43
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    @Bálint: There's a significant community that collects vintage computers. The community that collects S/3x & AS/400 stuff like this is a bit limited because it's harder to get an OS for an old S/38 than, say, an old DEC PDP-11. However, in that community, something like this would be a nice addition. P.S. - Please, just don't scrap it for the keyboard. These things are increasingly rare, and if you separate the keyboard, the rest is mostly useless. You can get any variety of really nice new mechanical keyboards for your PC; you can't use that terminal with anything but that keyboard.
    – KJ Seefried
    Apr 17, 2018 at 2:13
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I tried to locate some Youtube videos that quickly demonstrate what a 5250 terminal screen looks like. This one is pretty good:

https://www.youtube.com/watch?v=tn9xz1SpuyE

5250 is a block mode display system. The server sends out a blob of data to the terminal, which then by itself formats text in color in a pretty way at 80 columns by 25 lines.

The server also tells the terminal to create areas where the user can type things, typically displayed as an underlined area, and/or a list of function keys the user can press to send commands back to the server.

The user's terminal is pretty smart by itself, and handles all cursor movement and text entry without constant per-character hand-holding from the server as with a normal unix terminal session.

When you send data back to the server, it only sends back what is inside the editable areas.

The terminal protocol is designed to be as efficient as possible so that the server is freed up for actual work, so common commands are assigned to single-press function keys, and the function numbering goes up to F24, so there can be a huge number of them available at any time.

You can insert and delete characters in the editable text fields but you can't go over the limit of the field length. Because the display of data is so tightly locked down to the 80x25 display area, it is common for commands and names of things to be "smushed" into some very short abbreviation to fit in the limited space available in each column of data.

 

EDIT: An interesting side effect of 5250 and 3270 block mode terminal protocols is that they have a very similar modern equivalent... web pages with data entry fields.

It is possible to run a web server on an AS/400 that reformats 5250 / 3270 block mode directly into a web page, and reassigns function keys to clickable buttons on the page. With this, terminal hardware or a terminal program is no longer needed, but instead only a web browser.

For example:

https://www.youtube.com/watch?v=h0jUbmeV5YU

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  • Wow, thanks for sharing! That web-enabling of them is really interesting, I'd never have guessed that was going on!
    – Muzer
    Dec 5, 2016 at 17:42
  • @muzer: Yup...there's a whole ecosystem of products that provide a nice, modern web-based front end that maps to green-screen terminal abstractions on the back-end. A surprising amount of banking, finance, insurance, logistics, etc., are back-ended by these kind of systems. You want really old-school, check out the airline industry 'ALC' protocol stack, and realize that much of the modern airline reservation system is based on abstraction layers on top of a 6-bit character set, multidrop bisync protocol.
    – KJ Seefried
    Apr 17, 2018 at 2:23

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