21CTO

May 2, 2026 · Industry Insights

Microsoft Open‑Sources the Earliest 86‑DOS 1.0 Code – A Historic Look

To mark the 45th anniversary of DOS, Microsoft has open‑sourced the original 86‑DOS 1.00 kernel, early PC‑DOS snapshots, classic utilities like CHKDSK, and Tim Paterson’s handwritten notes, providing researchers and educators with a rare, fully documented view of the OS that became the foundation of MS‑DOS.