Making FreeDOS Smaller [video] | Hacker News Reader

Making FreeDOS Smaller [video]

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37 pointszdw12 comments

Tech Tangents has a video where he trimmed FreeDOS to run on an IBM 5150: https://www.youtube.com/watch?v=EOVLlMQs9f8

Is FreeDOS aiming to provide DOS compatibility with newer computers, or better experience for old ones? Would there be any upside to installing FreeDOS instead of MS-DOS on a retro PC?

A lot of vendor tools (think firmware flasher, diagnostic tools) for older hardware used DOS boot images (CD, floppy, USB, netboot, etc) because it gives lower level access to hardware. Some software/hardware combo is also "real time" which was "easy" in DOS compared to higher level managed operating systems. Shipping those tools as a boot disk required a DOS license. So this is a market FreeDOS took over a long time ago (like parallel port CNCs). Another niche is the emulators for old games. They still need "a DOS". Until recently there was no open source release of MsDOS, so using it was technically piracy, which make some otherwise legal things hard to redistribute (think a legit website selling roms). I have seen it "in prod" in small business when I was younger where they would have it in a VM to access their old accounting and CRM from the 80's when they had to look up some things because the file formats were obscure and proprietary (think 5-10 employees shops which have been doing the same thing for decades, like food processing or wood mills)

Retro computer enthusiasts tend to use the "real" MsDOS or other era correct DOSses, so this isn't really a market where FreeDOS is used much.

Also, you don't need a different DOS for newer computers. As long as it has a BIOS compat mode, most flavors of x86 DOS will run just fine. This might change is the 16bit mode gets finally removed. If something can't run DOS, then it's technically not a spec-compliant PC.

> Retro computer enthusiasts tend to use the "real" MsDOS or other era correct DOSses, so this isn't really a market where FreeDOS is used much.

As a retro enthusiast (and a FOSS supporter - full disclosure), I disagree. Whatever the project calls for, is what I would use - if a real era-correct DOS is called for, then I use that. If I want to use FreeDOS and it works well for that project, then I use that. I’m sure I’m not alone on this one.

> This might change is the 16bit mode gets finally removed. If something can't run DOS, then it's technically not a spec-compliant PC.

Manufacturers have been shipping devices without Compatibility Support Module for several years now, so I have many x86(-64) devices that can't boot into an DOS.

I suppose in theory a UEFI+CSM firmware could be flashed, but I'm not aware of anyone adding back in CSM support on devices shipped without it.

I expect this is referring to Intel's proposed X86S spec: https://www.intel.com/content/www/us/en/developer/articles/t...

You get the source, you can fix bugs yourself and contribute the patch upstream.

Can it be compiled with libre tools?

I'm afraid they rely on OpenWatcom [1], which is under the Sybase Open Watcom Public License version 1.0, which is considered open source by the OSI but non-free by Fedora, Debian and the FSF [2]

[1] https://freedos.org/about/devel/

[2] https://en.wikipedia.org/wiki/Sybase_Open_Watcom_Public_Lice...

Are there even any other free/libre C compilers that can produce 16-bit DOS binaries?

I assume gcc can do it, since gcc can target far smaller/more complex/more niche 8 bit architectures.

GCC (and clang) can definitely do it. We use it to write option ROMs in C in qemu. This code is compiled with the `-m16` option. This particular code references 32 bit registers using 66h prefix so wouldn't work on an 8086, but AFAIK that's not a general problem:

https://gitlab.com/qemu-project/qemu/-/blob/master/pc-bios/o...

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