It is possible though only software using standard I/O will work. You can do this using the ctty command - eg, CTTY COM1:

If you attempt this, be aware that DOS is pickier than other serial communications software in that the DSR line must be on. My premade null modem cables left it unconnected. (Instead, they connect DTR on one end with CD on the other). I connected the DSR and CD pins on the "DOS" end of the cable and it does work.

As davidrg mentioned the CTTY method works only with software that uses tty style calls to do I/O. Anything sophisticated or full screen will not and instead accesses the video card directly. There is some software (search for VMIX285.ZIP) which attempted to capture this and redirect to a serial port. I just tried it out, it somewhat works, but not very well, and is extremely slow. Forcing msd and edit to do monochrome mode sped it up a tiny bit but not enough to be usable. You'd also have to figure out how to map function keys and arrow keys on the terminal to the escape sequences that VMiX expects. Not fun.

It would make more sense to install some BBS software on your DOS machine designed to be accessed over serial and use that instead.

There's an alternative to DOS/CTTY.

It's PC-MOS/386. It has explicit serial terminal support. 🙂

PC-MOS/386 released under GPL

VMIX285.ZIP sounds interesting:

VMiX is a multitasking and multiuser environment for IBM PC's and PS/2's (PC, XT, AT, PS/2, EISA) compatibles. […]
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VMiX is a multitasking and multiuser environment for IBM PC's
and PS/2's (PC, XT, AT, PS/2, EISA) compatibles.

- Graphics and text modes are supported by the shareware version.
- Compatible with MSDOS 6.0 and DRDOS 6 relocation to high memory.
- Loader utility for moving TSRs or VMiX to upper memory.
- Load VMiX to upper memory without robbing DOS of precious space.
- Run communications software while executing other tasks.

A platform for point-of-sale systems, distributed database access,
process control, uplinks and downlinks.

- Distributed multitasking within a NET of several linked VMiX hosts.
- Flip console screens w/single hot key, and additionally 4 terminals.
- Start new windows by pressing Shift-Enter to end a command line.
- A configuration text file, VMiX.INI, for passwords and startup scripts.

The Shareware Version is bigger and slower than the 386 version because
it is coded in 8086 code, since it must run in all 8088 PCs, as well as,
286's and 386's, and because it carries about 10Kb of registration related
dead wait. The Shareware Version also can not be as efficient when using
extended memory for virtual tasks, but a user without a chronometer might
not be able to tell the difference. Other than those limitations, the
shareware version is identical in capability to the Commercial Version.

PC-MOS/386 is also nice.

There are also options which don't (to my knowledge) implement multi-tasking and were intended for use cases like connecting to your office computer when you're at home or on the road, like Norton pcANYWHERE or the Commute tool in Central Point PC Tools. They wouldn't provide you with the ability to have multiple users using the machine at once but could let you use the machine for the most part without a directly-attached keyboard and monitor. I've thought about using software like this to save space on my desk: rather than have a dedicated keyboard, mouse and monitor for a DOS machine, or use a KVM which can be unreliable (although I think I have a decent one now), just access it through another machine. Can't interact with the BIOS this way though unless I get SGABIOS loaded somehow.

Bit off topic but as far as remote control goes, there is also TINY which supports graphics under DOS to some extent. Works over TCP/IP. Doesn't support Windows 3.x though - in my testing it tends to crash the machine if you start windows while connected remotely. Host TSR is free for non-commercial use, client (java) is open source. The client currently requires an older version of Java but the bug it experiences with current java is probably not too hard to fix.

I've also used Proxy by Funk Software. Its proprietary software and probably pretty hard to find legal copies of it now - my copy came as part of the Seagate Desktop Management Suite. Works over both TCP/IP and IPX and can remote-control DOS, Windows 3.x and Windows 9x. I think its more geared to remote-controlling Windows though - IIRC the DOS portion only supports IPX and doesn't handle graphical DOS apps very well. The client for the version I have doesn't seem to support Windows NT (incl. 2000/XP/etc) either. Performance is very good though - much better than VNC. Still not good enough for for playing windows games remotely on my DX4-100 at least.

doshea wrote on 2022-06-25, 00:49:

There are also options which don't (to my knowledge) implement multi-tasking and were intended for use cases like connecting to your office computer when you're at home or on the road, like Norton pcANYWHERE or the Commute tool in Central Point PC Tools.

I've made a quick video about Commute a while ago, because I couldn't find a demonstration video anywhere.

For you and others who wonder how it was like :
https://www.youtube.com/watch?v=qydywJluNdI

Personally, I think it was pretty usable for what it was.
By 1990 standards, it was almost exciting even.
Imagine logging into your workstation from your weekend house via modem to fix some things, finish work or
run some simulation software. 😃

Edit: @davidrg Cool Windows 3.1x software selection! Thumbs up for MOD4WIN and Foxpro! 🙂👍
I'd like to recommend Profan, CA dBFast and Delphi 1.0, too!

Maybe some communication software like Balloon Telecom Manager that came with those Creatix modems etc.
And other common utils like WinGIF, Graphics Workshop, XNView, Paintshop Pro etc.
AutoSketch for Windows is fun, too, if you're into technical drawings.

If you're into ham radio, UI-View will run on Windows 3.1, as well.
https://www.youtube.com/watch?v=tzyQyCRyeWE

https://www.youtube.com/watch?v=7BLD1qIZQos

All it needs is an FM scanner or 2m band FM two-way radio and a TNC box.
The latter can be emulated on an other computer via sound card, also. DireWolf, MixW2 etc.
(Edit: Or just use WebSDR as a receiver.)

And then there are Fractals (WinFract) and astronomy software.
Back in the 90s, I used to use Skyglobe (DOS) and SkyMap (Win 3.x).. 😃

Jo22 wrote on 2022-06-25, 02:54:

Personally, I think it was pretty usable for what it was.
By 1990 standards, it was almost exciting even.

Yeah, it was good for what it was, not as good as pcANYWHERE but if you already had PC Tools it was a lot cheaper (because you already had it)!

If we're also talking about LAN-based remote control software, Commute could use IPX, and there was also pcANYWHERE/LAN (which cost almost 3x as much based on the one ad I just saw). I can't recall if they actually required a NetWare server for location - I think Commute might have but pcANYWHERE/LAN didn't?

The DOS version of pcANYWHERE could deal with Windows 3.x if I recall correctly. I can't remember about Commute.

There's a couple of interesting ones kicking around on SIMTEL and other MSDOS archives... not recalling a name right this second, but I made a mental note to go back and play with them sometime.

Personally, I'd like to dig out older WinCE versions of PCAnywhere and try using them with old PDAs and DOS machines. XP and up I think can use VNC, but that did start to be a "thing" earlier, and had 9x versions, but IDK if they're findable or very wise to use due to gaping security holes etc.

Another avenue is the multi user DOS extensions offered as part of some DRDOS installs, 6.0 up IIRC, or standalone products from earlier that might be archived in the usual kind of places.

One of the more obscure solutions for getting multiple users on a single PC was the Austin Buddy B-200/B-210. It was basically a special video card that had additional keyboard/mouse inputs.

I remember seeing ads for that sort of thing in the 80s, "Why pay $5000 to get each user a PC when you can have 4 users on 1 PC for only $500 per extra user" doing it with a mish mash of expansion cards, terminals and software.

This was in a time when simple serial terminals (glass terminals) were still around and less expensive than PCs.

Back then, terminals weren't just meant as input/output devices for microcomputers (say, CP/M PCs),
but also to service equipment.

And to dial into distant host computers via acoustic couplers and telephone line.
News reporters sent in articles to their news agencies that way, for example.

Terminals were also used to configure embedded devices, check communications devices (say ISDN) and so on.

They were the successor to electro-mechanical teletypes (TTY devices) essentially.

Early micro controller platforms (say, 8052 AH BASIC) were programmed via terminal, too.

Graphical terminals also existed, like those that supported the Tektronix 4010 and 4014 standards.

And of course to connect to a local big expensive not a PC computer.

I've got a MicroVAX 3500 that was originally bought in 1988 by the NZ Department of Scientific and Industrial Research to replace a VAX-11/780. It has three CXA16 async multiplexor cards to support a total of 48 terminals locally and more remote terminals via ethernet using the LAT protocol and DEC terminal servers. Was configured for VT320 terminals locally (the breakout boxes for the Multiplexor cards use RS423 MMJ connectors) but I only got a much older VT220 with the machine so possibly DSIR didn't bother upgrading their terminals at that site.

The newer terminals from DEC even support multiple sessions. My VT520 can have up to four going simultaneously - you can either cycle through them with a key on the keyboard, or you can do split screen with two of the sessions. To get the sessions into the terminal you can either use its three serial ports, or the proprietary TD/SMP protocol that can feed two separate sessions down one serial line from a DECserver terminal server (or perhaps an OpenVMS box directly).

Its a shame most terminals were just thrown in the bin. They're kind of hard to find these days.

davidrg wrote on 2022-07-11, 21:56:

Its a shame most terminals were just thrown in the bin. They're kind of hard to find these days.

Yeah, I always wanted one but by the time I started searching eBay they were already very expensive. I do have some sort of IBM AS/400 terminal, but that is far from a serial terminal - it needs some other specialised hardware I don't have in order to be of any use to me - so it's unfortunately just a waste of space and I plan to get rid of it.