Int 10 Fn FE  - Topview - Get Shadow Buffer                                [V]

   AH = FEh
   ES:DI -> assumed video buffer
       B800h:0000h color text/CGA graphics, B000h:0000h mono text,
         or A000h:0000h EGA/VGA graphics (RSIS environments only)

Return: ES:DI -> actual video buffer for calling process
Desc:  Determine the address of the virtual screen to which the program
     should write instead of the actual video memory; this permits
     programs to be multitasked without interfering with each other's
     output, and allows memory managers to move the video memory to
     permit larger programs to be loaded.

Notes: if no multitasker or RSIS-compliant environment is installed, ES:DI is
     returned unchanged; RSIS is the Relocated Screen Interface
     Specification
   for display pages other than 0, use AH=05h and AH=0Fh to determine
     whether a particular page exists
   TopView requires a call to AH=FFh to notify it that the screen has
     changed; DESQview will check for changes itself until the first call
     to AH=FFh

See Also: AH=05h,AX=5201h,AH=FFh,INT 15/AX=1024h,INT 21/AH=2Bh"DESQview"

See Also: INT 21/AH=ECh"DoubleDOS"