This was first unearthed copy of Microsoft's "multitasking" version of MS-DOS. It's since been copied to other web sites, but these are the original images, released on jsmachines.net in March, 2013. This version of MS-DOS was never officially released in North America. More information is available at Wikipedia and OS/2 Museum.
Note: The designation "4.0M" is not an official version number; it's an internal version number used only to differentiate these disk images from those of the official MS-DOS 4.00, released in June, 1988.
The IBM Model 5160 machine configuration below boots MS-DOS 4.0M. To access the MS-DOS "Session Manager" after it's booted, tap the Alt key.
IBM Model 5160
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