When speaking about MS-DOS, it involves a journey through the corridors of computing lore.
MS-DOS, or Microsoft Disk Operating System, was the operating system that revolutionized personal computing. Developed by Microsoft, it was initially released in 1981, marking the beginning of the PC era. And MS-DOS 4.0 was released in July 1988, amidst the bustling landscape of the late 1980s computing world.
It was a significant release.
This time, Microsoft works with IBM to release a 1998 uncompiled version MS-DOS 4.0.
After more than 35 years since the operating system made a muted appearance ahead of Windows 3.x, MS-DOS 4.0 finally came to the masses as an open-source project on GitHub.
MS-DOS 4.0 is a relic from when IBM and Microsoft made a joint development, in which the two companies contribute portions of the code
At the time the companies were in the throes of their joint OS/2 adventure, and that the operating system was developed during a somewhat difficult relationship between the two at the time led to two branches eventually being released.
It was notable for its support of FAT16 hard disk partitions greater than 32 MB and the addition of the MS-DOS Shell.
It was also one of the final outings for the SELECT setup program.
The project for open-sourcing MS-DOS 4.0 began when a researcher named Connor Hyde (aka Starfrost) was documenting the relationship between DOS 4, MT-DOS (Multitasking DOS), and OS/2.
Hyde contacted the Microsoft Open Source Programs Office (OSPO) to know whether the source code for them might be released.
The OSPO team was unable to find the full source code for MT-DOS, but they did find the source for DOS 4.
This was when Hyde got in touch with Microsoft Chief Technical Officer Ray Ozzie, who found the source code in his collection of floppy disks.
The disks in question, date back to 1984, and contain unreleased beta Multitasking DOS binaries, and also the ibmbio.com source code.
Scott Hanselman, a Microsoft VP Developer Community, received help from internet archivist and enthusiast Jeff Sponaugle, and managed to create images of these original disks and carefully scanned the original printed documents from this “Ozzie Drop”.
Subsequently, the team uploaded the code to GitHub under the MIT license.
"Microsoft, along with our friends at IBM, think this is a fascinating piece of operating system history worth sharing," the website post from Microsoft says.
According to Microsoft, the code can be run on an original IBM XT, a new Pentium, or within the open source PCem and 86box emulators.
MS-DOS -4 introduced some notable features over its predecessor.
One of the most notable, was the inclusion of a graphical shell called MS-DOS Executive, which provided a more user-friendly interface compared to the command-line interface of previous versions. This was Microsoft's attempt to make computing more accessible to a broader audience, although the execution wasn't as polished as later graphical interfaces.
It's worth noting that the open-source MS-DOS 4 on GitHub lacks the app-switching capabilities that landed it the nickname MT-DOS.
Rather, Microsoft and IBM have released the source code for a totally separate version of DOS 4.00, primarily developed by IBM to add more features to the existing non-multitasking version of DOS that ran on most IBM PCs and PC clones of the day.
Multitasking was scrapped in later versions to make way for GUI operating systems like Windows.
It's also worth noting that before this, Microsoft already released MS-DOS 1.25 and 2.0 in 2014, in cooperation with The Computer History Museum.