Recently, we’ve covered quite a bit of retro stuff for Windows that shows how modern apps have their roots in the 90s.

At the beginning of March, we reported on an interesting experiment that demonstrated the excellent backward compatibility of Windows 11 with the help of Office. A similar experiment was done by YouTuber but on a much larger scale, where he ported “thousands of apps” to Windows 95. We also covered the interesting story of the engineer who added Zip support to Windows, but was almost fired for that too.

If you’re a fan of Windows in the past, you’ll likely be happy about the latest announcement. Microsoft, in partnership with IBM, announced that it was 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 was designed with preemptive multitasking in mind, so specially written programs were able to run in the background.

However, it is interesting that this initial release, known as “Multitasking DOS”, was not widely released due to the lack of interest shown by OEMs of the time, including IBM itself.

Thus, the final MS-DOS 4.00 release version of 1988 was not the multitasking operating system it was originally intended to be.

Microsoft says they have successfully run MS-DOS 4.00 on an IBM PC XT within PCem (a Windows 95/98 emulator) as well as an 86box emulator (an IBM PC emulator).

Internet Archive and Internet enthusiast Jeff Spoonaugel, who among other things helped shoot the original disks (pictured above), today posted a YouTube video of DOS 4.00 Multi-tasking running on an IBM PC XT:

The source code is available at GitHub For those who want to try. You can learn more about the story at the source links below.

source: Microsoft Through Scott Hanselman