INT 21 - DR-DOS 5+ - DETERMINE DOS TYPE
        AX = 4412h
        CF set
Return: CF set if not DR-DOS
            AX = error code (see AH=59h)
        CF clear if DR-DOS
            DX = AX = version code (see AX=4452h)
Note:   this obsolete call which will not be supported in future versions of
          DR-DOS is identical to AX=4452h
SeeAlso: AX=4452h

.