Microsoft and IBM open source MS-DOS 4.00
Microsoft, in partnership with IBM, has released the source code of MS-DOS 4.00 under the open-source MIT license. This release comes a decade after Microsoft first made the source code for MS-DOS 1.25 and 2.0 available to the public through the Computer History Museum.
The decision to release the MS-DOS 4.00 source code was inspired by the discovery of early, unreleased beta binaries by researcher Connor “Starfrost” Hyde. Hyde’s discovery stemmed from a conversation with former Microsoft Chief Technical Officer Ray Ozzie, who unearthed the binaries among floppies sent to him during his tenure at Lotus. Intrigued by the software’s historical value, Hyde approached the Microsoft Open Source Programs Office (OSPO) to explore the possibility of making these resources publicly available.