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Microsoft Releases Original 86-DOS Source on GitHub

5/1/2026

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Summary

Story summary

Microsoft published the earliest DOS source code on GitHub on April 30, 2026.
The release includes the 86-DOS 1.00 kernel, PC-DOS 1.00 snapshots, and CHKDSK.
Microsoft bought 86-DOS (originally QDOS), hired creator Tim Paterson and rebranded it MS-DOS in July 1981.
Microsoft staff Stacey Haffner and Scott Hanselman announced the archive, saying the code was found in Paterson’s garage.
Open-source releases of MS-DOS 1.25 and 2.x occurred in 2018 and MS-DOS 4.0 in 2024.

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Story summary

Microsoft published the earliest DOS source code on GitHub on April 30, 2026.
The release includes the 86-DOS 1.00 kernel, PC-DOS 1.00 snapshots, and CHKDSK.
Microsoft bought 86-DOS (originally QDOS), hired creator Tim Paterson and rebranded it MS-DOS in July 1981.
Microsoft staff Stacey Haffner and Scott Hanselman announced the archive, saying the code was found in Paterson’s garage.
Open-source releases of MS-DOS 1.25 and 2.x occurred in 2018 and MS-DOS 4.0 in 2024.