Microsoft Releases Historic MS-DOS 4.0 Source Code in Collaboration with IBM

In an extraordinary move that bridges past and present software development landscapes, Microsoft, in partnership with IBM, has recently made the source code for MS-DOS 4.0 available to the public. This release comes more than 35 years after the operating system initially debuted, providing a glimpse into the collaborative efforts during the early days of personal computing.

MS-DOS 4.0, a significant milestone in the history of operating systems, was developed during a pivotal time when IBM and Microsoft were jointly working on the OS/2 platform. This version of DOS was especially notable for its introduction of the FAT16 hard disk partitions, supporting sizes greater than 32 MB, and the innovative MS-DOS Shell, enhancing user interaction with the system through a graphical interface. Another key feature was the SELECT setup program, marking one of its last appearances in the DOS series.

The discovery and subsequent release of the source code were spearheaded by Connor Hyde, also known by his alias Starfrost. Hyde was researching the interconnections between DOS 4, Multitasking DOS (MT-DOS), and OS/2 when he approached Microsoft’s Chief Technical Officer, Ray Ozzie. Ozzie, intrigued by Hyde’s inquiry, managed to locate the source code among his collection of historical floppy disks, some dating back to 1984.

These disks were not only a repository of the MS-DOS 4.0 source code but also contained beta versions of the Multitasking DOS binaries and the source file. Recognizing the potential historical value, Hyde reached out to Microsoft’s Open Source Programs Office (OSPO) to explore the possibility of making this software publicly accessible.

The endeavor to digitize and release the code was led by Scott Hanselman, Microsoft’s Vice President for the Developer Community, with assistance from archivist Jeff Sponaugle. They successfully imaged the disks and scanned the accompanying printed documents, although they were unable to locate the complete source code for MT-DOS. Despite this, the team proceeded to release the MS-DOS 4.0 source on GitHub under the MIT license, marking a significant contribution to the preservation and study of software heritage.

As part of the archival materials, Ray Ozzie’s personal files were also made available online, including detailed documentation of Multitasking DOS. This release provides invaluable insights into the development and operational specifics of MS-DOS 4.0 and its variants, offering both nostalgic enthusiasts and new programmers a chance to explore a key piece of computing history.

This historic release has been well-received within the developer community, with many expressing a renewed interest in the capabilities and impact of early operating systems. According to Microsoft, the newly released code is versatile enough to be run on an original IBM XT, a modern Pentium, or within popular emulators like PCem and 86box, ensuring that it remains accessible and functional for interested users across different hardware generations.

While the focus remains on celebrating this release, Scott Hanselman hinted that more could be on the horizon, with potential plans to release the source codes for MS-DOS versions 3.3, 5, and 6. This initiative not only honors the legacy of early software innovation but also fosters a deeper understanding and appreciation of the foundational technologies that have shaped today’s digital landscape.

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