Int 2F Fn F100  - Dos Extender Installation Check                          [E]

   AX = F100h

Return: AL = FFh if DOS extender present
       SI = 444Fh ("DO")
       DI = 5358h ("SX")

Note:  supported or soon to be supported by Phar Lap, Rational, Ergo, and IGC

See Also: AH=A1h,AX=ED00h,AX=FBA1h/BX=0081h,INT 15/AX=BF02h