TECH NEWS – It’s rare to see Microsoft release the source code for one of its operating systems, but the Redmond-based company does it occasionally.

Instead of thinking that Microsoft has released the source code for Windows 8 or Windows Vista (which might be exciting, since it would allow you to “fork”, i.e. create new branches in its development, and add modern functionality that is used today; this could be especially popular for Windows 7), you should think about a code package that is a bit older than that.

Microsoft, along with IBM, released the source code of MS-DOS 4.0. Windows Millenium Edition was the last DOS-based release; Windows XP and later OSes are all based on the NT kernel, putting DOS to rest. Version 4 of MS-DOS was released in 1986 (and because relations with IBM were not so good, they released their own version, known as IBM DOS 4.0), and the Computer History Museum released versions 1.25 and 2.0 in 2014, and these source codes are available on GitHub. MS-DOS 4.0, sometimes referred to as European MS-DOS 4.0, supported the New Executable file format and preemptive multitasking, but retained many of the limitations of MS-DOS 3.0, such as not being able to use more than 640 KB of memory. (16 GB is the standard today. 26214.4 times the 640 KB…)

A researcher contacted Microsoft because he had found some unreleased beta binaries of DOS 4.0 on some old floppies left over from when he worked at Lotus. He digitized them and found that they were unreleased versions of the operating system. Using some printed documents, he scoured the Microsoft archives and eventually found the complete source code. Microsoft was able to run it on an original IBM PC XT, a “newer” Pentium, but also had success on open source PCem and 86box emulators.

When will we get this on the newer version of Windows?

Source: PCGamer, Microsoft, GitHub