It's no joke. Microsoft and IBM have joined forces to open-source the 1988 operating system MS-DOS 4.0 under the MIT License.

[Yeo Kheng Meng] didn’t cheat by simply running MS-DOS on a modern PC, either: he tested the client on a real 1984 vintage IBM 5155 Portable PC. This semi-portable PC/XT model sports a 4.77 MHz ...

He still oversees the project to this day. MS-DOS, IBM-DOS, and other DOS derivatives were the most popular operating systems for PCs from the first IBM PC in 1981 to around the mid-1990s.

but of more surprise is that IBM had a multitasking DOS called TopView, or even that Microsoft themselves released the fully multitasking MS-DOS 4.0. We remember DOS 4 as being less than sparkling ...

The original operating system for IBM PC compatible computers ... When people use the term DOS, they are commonly referring to Microsoft DOS or MS-DOS. This term was viewed 8,059 times.

The software was formally introduced under its new name in 1983 as a graphical user interface for the MS-DOS operating system running on IBM PCs and those compatible. Until Windows 95, the ...