The "early Windows compatibility" problem with DR-DOS happened in a Win3.1 beta. see https://en.wikipedia.org/wiki/DR-DOS#DR_DOS_6.0_/_Competition_from_Microsof

The "early Windows compatibility" problem with DR-DOS happened in a Win3.1 beta. see https://en.wikipedia.org/wiki/DR-DOS#DR_DOS_6.0_/_Competition_from_Microsoft https://en.wikipedia.org/wiki/DR-DOS#DR_DOS_6.0_/_Competitio... I don't think Microsoft designed/tested Windows to run on anything other than MSDOS/PCDOS.