Weird old legacy hardware that only runs on DOS generally requires real-time access to stuff like ISA cards or parallel/serial ports, so this wouldn't work for that use case since the computer doesn't have any of those.

I have a weird old nylon cutting machine connected to a DOS machine over a serial port. It would not work with a USB/RS-232 adaptor?

USB-serial conversion would add a measurable amount of latency, and the access to USB hardware would occur under a non-real-time OS. Whether the setup "works" would be highly hardware-specific. There are modern industrial "PC" boards that are essentially a i586 implementation in a SoC and can run these workloads far more reliably, while consuming a lot less power compared to old x86 hardware. (They're also of interest to retrocomputing enthusiasts, for largely the same reasons.)

It probably won't if they do weird things with the flow control pins or if the timing really matters, but serial is far more likely than parallel to keep working.

Yeah this is why industrial PCs still have those physical ports.

Depends on the adaptor too. Cheap ones only have Rx and TX pins . The rest of the pins are not connected. If your device only used Rx and Tx it would work fine . If it uses functionality of other pins make sure you get the right adaptor

Spend no less than $20 on a USB to serial converter and you'd probably be fine. Anything with an FTDI chip in it are the best. Anything with a Prolific chip has a good possibility of being counterfeit will either not work well or the legit driver will try to brick it.

FTDI pushed driver updates that bricked counterfeits... https://www.theregister.com/2016/01/31/ftdi_accused_of_brick...

That's orecisely how we run our thread 3D printer. It even has a serial (UART) to USB chip on board and it's connected to a RPi3 boc running Linux and Octoprint.

No, the FreeDOS HP option has always been used by the customers who did not want to pay a Windows license, because they wanted to install a different operating system, usually some Linux variant (the option to install a pirated Windows variant was also popular in some parts of the world).

Dell has the Ubuntu option for many computers, but for those who do not want to use Ubuntu, like myself, there is no difference between the Dell Ubuntu option and the HP FreeDOS option, because such customers will always install their own preferred OS, immediately after the purchase of a new computer.

I'm the author of the article; It's not actually usable for that. The way the Qemu VM is setup there is no way to interface with the outside world at all. The only way to get any data in or out of that VM is through the keyboard and screen.

Would those apps work inside QEMU though? Is it configured to properly pass through the parallel port?

Maybe, but wouldn’t the customer have to know how to run QEMU? I am imagining a customer who wants to just replace an old machine while changing as little as possible.

Since this install is based on QEMU running in Linux, it would not meet that need.

The end user need not know it is QEMU atop Linux. They see and use DOS.

Yes, but inside a VM. What access to real hardware (e.g. to communicate with the outside world) does the user get?

Whatever is configured with QEMU: everything if that was the use case.

But it looks like their setup is not configured to give access to hardware, at least I didn't see any options on the command line.

Highly unlikely, without really messing around with it.

FreeDOS is known to not run well inside of virtualization. A proper host install would be far more capable.

That is not true.

In fact, if you just boot FreeDOS 1.3 in VirtualBox, you'll see it detect the virtual NIC, load a TCP/IP stack and acquire an IPv4 address, then report it.

It is mostly developed and run inside VMs these days, AFAICS.

But a proper host install is not possible on modern hardware.