Int 2F Fn 48C1  - PCed/vstack - Installation Check                         [-]

   AX = 48C1h
   BL = 00h

Return: AX = 0000h if installed
       BX = VSTACK resident segment
Program: VSTACK is a resident backscroll utility included as part of the PCED
     package

Note:  chains if BL <> 00h on entry

See Also: AX=48C0h,AX=48C2h