Microsoft open-sourced MS-DOS 4.0.

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Today Microsoft open-sourced MS-DOS 4.0.

You can check it out here: https://github.com/microsoft/MS-DOS

MS-DOS v1.25, v2.0, v4.0 Source Code
This repo contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0, plus the source-code for MS-DOS v4.00 jointly developed by IBM and Microsoft.

The MS-DOS v1.25 and v2.0 files were originally shared at the Computer History Museum on March 25th, 2014 and are being (re)published in this repo to make them easier to find, reference-to in external writing and works, and to allow exploration and experimentation for those interested in early PC Operating Systems.