Int 21 Fn E400  - Doubledos - Installation Check/program Status            [T]

   AX = E400h

Return: AL = program status
       00h if DoubleDOS not present
       01h if running in visible DoubleDOS partition
       02h if running in the invisible DoubleDOS partition

See Also: AH=E5h"DoubleDOS",AX=F400h