On April 25, 2024, Microsoft released the source code of MS-/PC-DOS 4.00 to the public, and the community managed to provide MS-DOS 4.01 as well.

While the original release was available as a set of six 5,25" floppy disks (and optionally three 3,5" disks for version 4.01), this open-source release does not have official installation media.

Recreating the original media would theoretically be possible, but I want to focus on the 720k images for this project. Having to swap around six floppies multiple times isn’t practical. Furthermore, we can build images for 1.44 MB floppy disks for increased compatibility: The SELECT utility used for the installation process doesn’t like it if you install it on floppies with a different format than the source disks are written in.

The open-source release is missing a few program files and the entire DOSSHELL environment, so that’s something we also have to deal with.

March 1995. Although PCs had been around for many years at this point, less than 40% of households in the US owned one. Back then, people mostly associated PCs with being a machine used at work, not a thing you’d even need at home. They were complicated and… unfriendly.

Just a few months before the launch of the all-new Windows 95, Microsoft Bob was an attempt to create a user-friendly interface that runs on top of Windows to increase the popularity of PCs at home and show how valuable a PC might be for purposes other than business.

Today, I’m excited to finally announce a new side project I’ve been working on for quite a while.

To be more precise, this will be our new side project that we’ll be working on in the future.

Introduction

Have you ever noticed that a pixel-perfect screenshot from a virtual machine running MS-DOS in the default VGA text mode looks slightly off? The characters are too wide, and the whole image seems stretched.

At the very least, it doesn’t evoke the same nostalgic feeling as the old CRT days, does it?

But did you know that what you’re seeing is a perfect representation of the actual image, while your monitor from 1995 was deceiving you? Let’s have a closer look.

Do you know what computer games and the Voyager space probes have in common? Clever engineering can extend their missions way beyond their intended lifetime.

3D Pinball for Windows – Space Cadet, the iconic game bundled with the Microsoft Plus! packs and included in Windows NT4 up to Windows XP, is preserved for decades to come thanks to a reverse engineering project by Andrey Muzychenko.

Andrey’s work involved decompiling the executable that shipped with Windows XP and creating a modern reimplementation using SDL2 . This means you can now enjoy both the bundled version and the ‘Full Tilt! Pinball’ version on Windows, Linux and macOS.

A couple of weeks ago, Microsoft released the source code of MS-/PC-DOS 4.00 to the public.

Due to various bugs, DOS 4.00 was a relatively short-lived release, and it was replaced by DOS 4.01 just a couple of months later.

Howard M. Harte (hharte), who already fixed various flaws in the official source code release of MS-DOS 4.00 , managed to figure out the differences between DOS 4.00 and 4.01 — we now have access to the improved version as well!

On April 25, 2024, Microsoft released the source code of MS-/PC-DOS 4.00 to the public.

While this release is exciting and essential to computing history, Microsoft’s release process was not entirely flawless: An accidental conversion from codepage 437 to UTF-8 destroyed parts of the source code and caused build failures.

In less than a week, on April 30, 2024, the community provided all necessary patches to restore the source code to its original state, matching the 1988 release of MS-DOS 4.00.

A brief introduction

I launched my Daily MS-DOS command bot a few months ago.

The initial idea was straightforward: Pick a random command or program that ships with MS-DOS 6.22 and post a brief description.

With a bit of help from some websites that archived the MS-DOS reference manual, I finished the initial revision of the JSON-based data file including all the comments with a short description in a matter of hours. I wrote a simple Bash script to pick a random command, fetch the description from the JSON file, and publish a post through the Mastodon API.

Easy. But shortly after that, a question arose: “What about screenshots?”

At first, I thought about going through every command in my data file, spinning up a VM, executing the command, taking a screenshot, and linking to it in the data file itself. While this approach is possible, it is tedious. There’s no real challenge in repeatedly typing in commands and trying to keep track of the screenshots I already took. Moreover, any change in the command list would require spinning up a VM, executing the command, taking a screenshot, and modifying the data file to include the modified screenshot.

But what if I could do all of this dynamically by taking screenshots at the moment my MS-DOS VM is executing the command I requested?

Microsoft released the last standalone version of MS-DOS as MS-DOS 6.22 in 1994.

Even though this operating system is decades old and a true relic of the past, people still develop new software for it. Thanks to a couple of modern tools, we can connect MS-DOS to the internet. Since just having a connection to the outside world itself is pretty boring, we connect MS-DOS 6.22 to something fairly modern and amazing: the fediverse.

Let’s have a look.

In my previous article , I described how I managed to install Windows 2000 in DOSBox-X.

Even though this experiment was successful, I was not really with the results. While I got Windows 2000 working, I didn’t want to stop there. The final goal for the project was to get Windows XP running instead. However, after multiple attempts I gave up, thinking that Windows XP was impossible to use.

Well - I was wrong. But let’s start at the beginning.