Microsoft Releases 86-DOS and PC-DOS 1.00 Source, Opening Its Earliest OS Code

Overview

• Microsoft published the 86-DOS 1.00 kernel and PC-DOS 1.00 development snapshots under a permissive license on GitHub.
• The trove includes utilities such as CHKDSK plus assembler listings, including the assembler’s own source.
• Much of the earliest code survived as printer-paper listings kept by 86-DOS author Tim Paterson and was scanned and transcribed for release.
• Microsoft says the collection shows how DOS was built for early 8086 machines and helps clear up long-standing version numbering questions.
• The release builds on earlier MS-DOS source drops and documents the 1981 path from 86-DOS to IBM’s PC-DOS that set up Microsoft’s rise in PCs.