Microsoft and IBM released MS DOS 4.0 source code

Microsoft and IBM joined together and released MS DOS 4.0 source code under MIT license. Microsoft partnered with IBM for features related to multi-tasking in MS DOS. Multitasking DOS did not see a wide release. 

Former Microsoft Chief Technical Officer Ray Ozzie has found unreleased beta version of the DOS 4.0 was available in his floppies. Starfrost a researcher doing research on MS DOS Multitasking, Ray and Starfrost were chatting about the MS DOS Multitasking and Starfrost got to know about the floppies having source code of MS DOS 4.0.

Starfrost reached out to Microsoft Open Source Programs Office and explored the option to release the software as open source. Few others from Microsoft joined hands and explored the Microsoft Archives and Ray's floppy collection. They were not able to retrieve full source code for MS DOS Multi-Tasking but they were able to recover full source code for MS DOS 4.0.

Ten years ago, Microsoft released the source for MS-DOS 1.25 and 2.0. All the source for MS-DOS 1.25 and 2.0 was written in 8086 assembly code. Now they came forward and released MS DOS 4.0 source code as open source under MIT license in Github. This is really a good initiative. It will allow students to learn about the basics of operating systems.