This is not that. This is the road not taken, at least not by IBM and compatibles.
At the time, Microsoft assumed that DOS as we know it would never live past version 3. This was their idea of what DOS 4 should be. A new major version breaking strict compatibility. What we know as OS/2 1.x was originally named DOS 5, another new major "DOS" version breaking strict compatibility.
This Multitasking MS-DOS never took off except in niche applications, and OS/2 eventually got its own product name which is why there were then regular DOS releases 4 and 5 followed by 6 and eventually 7 become part of Windows 95.
For example, the src/BOOT/MSBOOT.ASM file has a revision history including 3.31 and has code for the 32-bit sector count.
But more to the point the src/CMD/IFSFUNC folder contains the code for the IFSFUNC.EXE which only exists on IBM DOS 4.
So it would seem that the pdf folder has absolutely nothing to do with the source code, it's just an archeological bonus.
...which was buggy and quickly followed by 4.01
Are they releasing the source to 4.01 too? Would be neat to see a diff of those.
> MS-DOS 4.0 (multitasking) and MS-DOS 4.1 – A separate branch of development with additional multitasking features, released between 3.2 and 3.3, and later abandoned. It is unrelated to any later versions, including versions 4.00 and 4.01 listed below
