The iconic DR-DOS operating system has been resurrected by a company called Whitehorn Ltd., which is developing a complete clean-room reimplementation from scratch. Unlike previous open source versions, this new DR-DOS 9.0 is proprietary and offers only binaries, raising questions about its relationship to the original legacy.
DR-DOS, the legendary DOS-compatible operating system that once challenged Microsoft's dominance, has been resurrected by a company called Whitehorn Ltd. The new version, DR-DOS 9.0, represents a complete clean-room reimplementation built from scratch rather than being based on the original Digital Research codebase.
According to the developer behind the project, who goes by the Reddit username CheeseWeezel, this is "a totally new codebase built to honor Gary Kildall's vision" with "no EDR-DOS code, no FreeDOS code, no Caldera code." The developer claims to own the DR DOS trademark and rights, positioning this as a legitimate continuation of the original lineage that began with Digital Research in 1988.
The legal landscape of DR-DOS
The history of DR-DOS is complex and legally nuanced. The original operating system was developed by Digital Research and later acquired by Caldera, which in the late 1990s released the kernel source code in what was described as one of the earliest uses of the phrase "open source." However, as copyright owner Bryan Sparks clarified in 2022, the rights granted were not a formal open source license but rather a "fair, reasonable, and non-discriminatory" right to use, distribute, modify, and enhance CP/M and its derivatives.
This distinction matters because it means the original source code, while available, doesn't meet modern Free Software or Open Source definitions. The code is controlled by a complex license and is merely "source available" rather than truly open.
What's new in DR-DOS 9.0
The current development version, 9.0.291, is described as 100% assembly using NASM with ld86, targeting 386 processors and above. This means it won't run on vintage 8086 or 80286 machines, unlike some earlier versions of DR-DOS that were optimized for older hardware.
The developer reports that the system has been tested with various classic games and applications including DOOM, Warcraft, SimCity, Stronghold, Commander Keen, and Oregon Trail, with "lots works" but "still gaps" remaining.
Proprietary approach raises eyebrows
Unlike previous versions of DR-DOS that had some form of source availability, this new incarnation is being developed as proprietary software with only binaries offered to users. The developer acknowledges using AI for documentation and unit testing while focusing on the core development work.
This approach has drawn criticism from some in the retro computing community. One commenter noted that calling it "DR-DOS 9" is "at the very least cheeky" given that it's not actually a successor to the withdrawn version 8.1 but rather "version 0.9 of a whole new product."
The open source alternative
For those interested in a truly open source DOS-compatible operating system, SvarDOS offers a mature alternative. SvarDOS is based on the modernized EDR-DOS kernel, which itself derives from the Caldera-released source code. The developer behind DR-DOS 9.0 acknowledges that "SvarDOS is more mature and practical right now" while positioning their project as offering "long-term legal clarity and a direct link to DR DOS history."
Why this matters
The resurrection of DR-DOS under proprietary terms highlights the ongoing tension between preserving computing history and the realities of modern software development and business models. While the original DR-DOS was celebrated for its technical excellence and compatibility, this new version represents a different philosophical approach.
For retro computing enthusiasts and those interested in the history of personal computing, DR-DOS 9.0 offers an intriguing glimpse into what a modern, legally unencumbered implementation of the classic operating system might look like. However, the proprietary nature and lack of source code availability may limit its appeal to the open source community that has kept similar projects alive.
As development continues in private, it remains to be seen whether Whitehorn will eventually release source code, add modern features like UEFI boot support or GPT partition table compatibility, or maintain DR-DOS 9.0 as a purely proprietary product. For now, the project stands as a fascinating experiment in balancing historical preservation with contemporary software development practices.
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