Microsoft explains how you can run MS-DOS 4.00 that it officially open sourced today

Recently, we have been covering quite a lot of retro stuff for Windows which shows how modern apps have their roots in the "90s.

In early March, we reported on an interesting experiment which demonstrated the excellent backward compatibility of Windows 11 with the help of Office. A similar experiment was done by a YouTuber but on a much grander scale, where he ported “thousands of apps” to Windows 95. We also covered the interesting tale of the engineer who added Zip support to Windows but nearly got fired for it too.

If you are a fan of the bygone era of Windows, you are likely to be delighted about the latest announcement. Microsoft, in collaboration with IBM, has announced that it is open-sourcing MS-DOS 4.00 as the two worked together on the underlying code.

MS-DOS or Microsoft Disk Operating System was first released in 1981, which was 43 years ago. Later, in 1986, MS-DOS 4.00 was announced and it was designed with preemptive multi-tasking in mind such that specially written programs were able to run in the background.

Interestingly though, this initial release, referred to as "Multitasking DOS," was not released widely as a result of the lack of interest shown by OEMs of that time, including IBM itself.

Thus the final MS-DOS 4.00 release version from 1988 was not the multi-tasking OS it was once originally intended to be.

Microsoft says it successfully ran MS-DOS 4.00 on an IBM PC XT inside PCem (a Windows 95/98 emulator) as well as an 86Box emulator (an IBM PC emulator).

Internet archivist and enthusiast, Jeff Sponaugle, who, among others, helped image the original disks (photo above), published a YouTube video today of DOS 4.00 Multi-tasking running on an IBM PC XT:

The source code is available on GitHub for those who wish to try it. You can learn more about the story on the source links below.

Source: Microsoft via Scott Hanselman