INT 21 - DoubleDOS - INSTALLATION CHECK/PROGRAM STATUS
AX = F400h
Return: AL = 00h if DoubleDOS not present
= 01h if running in visible DoubleDOS partition
= 02h if running in the invisible DoubleDOS partition
SeeAlso: AH=F5h"DoubleDOS"

See also: 21E400

21F400 - DoubleDOS - INSTALLATION CHECK/PROGRAM STATUS