Chapter 1: The Open Sourcing of MS-DOS

On April 25, 2024, a significant announcement was made on the Microsoft Open Source Blog by Scott Hanselman and Jeff Wilcox. Scott, who serves as Vice President of Developer Community, along with Jeff, the Head of the Open Source Programs Office, shared exciting news about MS-DOS.

Their post highlighted the contributions of Ray Ozzie and Mark Zbikowski. Ray Ozzie is notably recognized as the originator of the executable file format. For those curious, you can verify this by checking the headers of any EXE file on your Windows computer. For example, opening Notepad2.exe in Notepad2 reveals that the first two characters are "MZ," which stand for Mark Zbikowski.

The blog post elaborated on how Ray Ozzie discovered floppy disks containing MS-DOS 4.0, prompting the decision to open source it. For those unfamiliar, floppy disks resemble primitive cloud storage, featuring a magnetic disk for data retention. The most common floppy disk could hold about 1.44 MB of data, which was used to distribute early versions of software like Windows. However, the disks containing MS-DOS were even older.

The release of the source code was met with enthusiasm as it represents a key chapter in software history. However, not everything went as planned.

Michal Necasek, who manages the OS/2 Museum website focusing on software history, was eager to analyze Microsoft's release. Unfortunately, upon further inspection, he discovered that the published files were converted to UTF-8, leading to issues that compromised the integrity of the source code.

Moreover, it appeared that the files did not originate from the original IBM DOS 4.00 released in June 1988, but rather from DOS 4.01. This suggests that what was released was a quiet update to DOS 4.01, which Microsoft had modified to avoid customer confusion over the earlier 4.00 version.

The findings were disappointing, suggesting that no substantial news had emerged from the release. However, as Michal pointed out, DOS 4.01 still holds significance.

The ensuing discussions revealed important insights. Firstly, such files are not suitable for Git, as this could lead to corruption. Michal recommended sharing them as ZIP files instead. Additionally, the source files were altered, notably with the removal of timestamps, which diminishes the value of the historical data.

Some sections of the source code were also censored. For instance, a comment that included a developer's name was edited to a vague reference, indicating a potentially hostile remark. Others noted that the source code had simply been relocated.

Overall, this release is a valuable piece of computing history. It's commendable that Microsoft has chosen to make it available, allowing archivists to delve deeper into its significance. While it may seem like a small step, having access to the original system can pave the way for the revival of applications built for it and unlock further historical software treasures.

The first video discusses the implications of MS-DOS being open-sourced, showcasing the journey of building and running it.

The second video delves into Microsoft's ongoing commitment to open-source initiatives, highlighting another operating system's transition to open-source status.

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